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4/16/2014 11:20 P.M. ET

Prospects Harvey, Giolito impress in pitchers' duel

In a South Atlantic League pitchers' duel that lived up to expectations Wednesday, the Orioles' No. 4 prospect Hunter Harvey slightly edged the Nationals' No. 1 prospect Lucas Giolito. But both young aces were long gone from the game by the time Delmarva defeated Hagerstown, 1-0, in walk-off fashion in the 15th inning.

Harvey, the Orioles' 2013 first-round pick, struck out seven batters in six shutout innings. The right-hander retired the first seven batters of the game before giving up the lone hit he allowed on the afternoon.

Through three starts this season with Delmarva, Harvey has a 1.06 ERA and an 18-to-4 strikeout-to-walk ratio in 17 innings.

Giolito, the Nationals' 2012 first-round pick, was also in peak form Wednesday. The right-hander allowed two hits in five shutout innings and struck out six.

But even with Harvey and Giolito out of the game, neither team's offense was able to break through for a run until the 15th inning. First baseman Trey Mancini started the winning rally with a two-out single and scored two batters later when third baseman Drew Dosch lined the game-winning hit to left field. Like Harvey, Mancini and Dosch are members of the Orioles' 2013 Draft class.

Harper a late scratch in Miami with tight left quad

MIAMI -- Nationals outfielder Bryce Harper was a late scratch with left quad tightness about an hour prior to Wednesday night's finale at Marlins Park.

Harper, who left the previous two games with the same issue, has hit 10-for-19 (.556) with three doubles, a triple, three runs and an RBI on the Nationals' two-city road trip, which concluded with a 6-3 win over the Marlins.

Harper told reporters after Monday's game that the quad had been tight since Friday, but it was "nothing too serious." During batting practice, he mentioned to manager Matt Williams that it was still bothering him.

"Bryce is in it for the long run, so I decided to get him out of there [Wednesday] just to make sure," Williams said. "He's been playing center field, he's been running a lot, he's been doing a lot of things. Give him a day to just calm it down a little bit. I expect him to be in there [Thursday]."

Nate McLouth was inserted into center field batting leadoff, while third baseman Anthony Rendon moved to second in the order. Tyler Moore got the start in left in Harper's place.

Souza cherishes long-awaited first MLB hit

MIAMI -- Despite Tuesday's loss, there was a bright spot late in the game for the Nationals.

Steven Souza Jr., who replaced Jayson Werth as a defensive substitution in right field in the sixth, singled up the middle off Dan Jennings two innings later for his first Major League hit.

"It's an exciting moment," said Souza, who will give the ball to his parents. "I just want to thank Jesus Christ, my Lord and Savior for putting me in this position and giving me an opportunity to come out here. It's an exciting moment for my family."

The 24-year-old, rated Washington's No. 14 prospect by MLB.com, earned his big league callup on Saturday when Denard Span went on the seven-day concussion disabled list. His hit came in his third at-bat since then.

A third-round pick in the 2007 First-Year Player Draft, Souza Jr. battled through several injuries and a 50-game suspension for testing positive for performance enhancing drugs in 2010.

"Everything that came together at this point," Souza Jr. said. "It's one of those things you've come so far and the hard work and the people that helped me along this way. It's a moment to share kinda with everyone.

"It's so cool, man. The love you get around here. The camaraderie. I'm just a new guy up here. Everybody is making me feel so welcome. To get hugs from [Ian Desmond], who I started with, to [Tyler Moore], one of my best friends. It's just a moment I'll never forget."

Walters records another career first vs. Marlins

MIAMI -- Marlins Park has become a place of milestones for Nationals shortstop Zach Walters.

On Sept. 6, 2013 in his Major League debut, Walters made a pinch-hit appearance and broke up Jose Fernandez's no-hitter with a slow roller down the third-base line in the sixth for his first career hit.

Tuesday night, Walters connected on a leadoff home run to right in the ninth on the first pitch from lefty Dan Jennings for his first big league dinger.

"It was great," said Walters, who entered as a defensive replacement in the sixth. "I asked Matt [Williams] if I could swing, didn't know if I was taking a strike, but got a fastball looking forward and just made good contact."

The Nationals acquired Walters, their No. 6 prospect according to MLB.com, in a 2011 trade with the Diamondbacks for right-hander Jason Marquis. Walters is now 4-for-11 (.364) with three runs, a homer and two RBIs in 10 Major League games.

Walters, who said his name has been spelled wrong for previous milestone balls, would probably use this one as a desk piece.

"The whole thing's a dream, honestly, just being here," Walter said. "My dream is to win the World Series. Hopefully I can talk to you about that later. … I don't remember any of it. I blacked out. They hit me on top of the head, just slapping hands. Before I know it I'm sitting on the other side of the bench."

Williams appreciates Harper's boldness on bases

MIAMI -- Even in a lopsided affair Tuesday night, the Nationals showcased their aggressiveness on the basepaths.

Down by 11 in the eighth inning, Bryce Harper singled to left field and advanced to second on Dan Jennings' wild pitch to the next batter. When Steven Souza Jr. singled up the middle, Harper held at third until he saw Marcell Ozuna's throw to the infield trickle away from cutoff man Garrett Jones. Harper scored Washington's first run on the play.

"We just allow the guys to use the tools they have," Nationals manager Matt Williams said. "That's what we hope. Of course we want to be smart about it. Of course we don't want to run into an out and all of that. Sometimes it's going to happen."

Williams said that he has daily conversations with Harper about the good and bad things he did the previous day.

A few times, Harper has been overly aggressive and gotten thrown out. That happened last Saturday when Taylor Jordan struck out on a missed bunt and Harper got caught stealing third. Still, there have been three or four instances when Harper has taken an extra base.

Last Thursday, Harper raced from first to third on a groundout to second against the Marlins. Williams believes the "haywire" plays get talked about instead.

"This game is never 100 percent and nobody ever will be," Williams said. "You take that chance sometimes. That's part of our DNA, that's the way we want to play and we can't change that. I want our aggressive guys and athletic guys to use their athleticism.

"You can't take away that from him or us either. That's the style of play that we want to play. We still want to maintain aggressiveness. We still want to be a team that we are. If we can do that then over the long run I believe that we have a really good chance to win. You can't just go opposite end of the spectrum because it's part of our game."

Nationals not worried about rotation's slow start

MIAMI -- One of the more surprising developments early on this season is the struggles of Washington's starting pitching.

After right-hander Stephen Strasburg allowed six earned runs on eight hits over four innings on Tuesday, the rotation's ERA rose to 5.06 for 26th in the big leagues. Last year, the Nationals posted the seventh-best ERA at 3.60.

"I think that's kind of how it works. We've had some dominant years in the past and teams are constantly trying to adjust on us," Strasburg said. "It's our turn to adjust on them. ... Everybody's stepping up their game to face us. It's our job to get to work and get back on track. I'm not really worried about it. We're swinging the bat really well, consistently here. As long as we can minimize the damage a little bit we'll be OK."

Since opening the season with two quality starts over the first three games, the Nationals have just three over their last 11 contests.

As a result, the bullpen has been taxed. Relievers have thrown the third-most innings (50) in the Majors. They have managed to record the fourth-best ERA (2.52) despite the heavy workload.

"They're good pitchers. Obviously they're not perfect," shortstop Ian Desmond said. "Something we'll deal with. It's nothing anyone here is worried about. We know what they're capable of. Offense has to be better too."

Worth noting

• Center fielder Denard Span, who is currently on the seven-day concussion list, flew back to Washington on Wednesday morning to visit the team doctor.

If Span passes the tests, he will go on a rehab assignment Thursday. The location depends on the weather forecast. If he feels good following that game, he will be pushed from three up to four at-bats on Friday.

"If he gets through those two games he should be fine," Williams said. "We'd like him back as quickly as possible for sure."

• Utility player Kevin Frandsen felt a spasm in his back on the final at-bat of Tuesday night's 11-2 loss. Frandsen told Williams on Wednesday he was fine.

"He reported with all his work to have no issues," Williams said. "He's not in the starting lineup [Wednesday], but he's available."

• According to Williams, outfielder Scott Hairston continues to progress on schedule. Hairston went on the 15-day disabled list on April 6 with a strained left oblique. He has not swung a bat yet.

"He's progressing into rigorous activity," Williams said. "Those things are tough. You've got to make sure you're really careful because if you have an additional setback it takes a long time."

• Right-hander Doug Fister will pitch two innings in an extended spring training game on Thursday in Viera, Fla.

Fister, who tossed 50 pitches in a bullpen session Monday, left Wednesday. The hope is to get him back on a rotation schedule. Williams expects Fister to periodically fly back to Washington to check on how he feels.

"Plan right now is we'll wait five days," Williams said. "After that he'll do that again in extended increased to three innings depending on workload, and then we'll send him out for a four-inning or five-inning rehab start. He should be good to go if all goes well. That's the tentative plan. It's not written in stone because you don't know how he's going to feel. It may even turn bigger than that depending on how it goes."

Christina De Nicola is a contributor to MLB.com. Teddy Cahill is a reporter for MLB.com. Follow him on Twitter at @tedcahill. This story was not subject to the approval of Major League Baseball or its clubs.