Jordan Zimmermann has been no slouch, either.The right-hander takes the mound Sunday at Fenway Park as surging Washington looks to complete the sweep by sending Boston to its sixth loss in seven games.Strasburg struck out 13 over six innings of a 7-4 win Friday, then Gonzalez followed by allowing two runs in 6 1/3 innings of Saturday's 4-2 victory. Adam LaRoche hit his 10th home run, but the pitching staff remained the story.The NL East-leading Nationals (34-23), winners of five of seven, lead the majors with a 2.97 ERA.Zimmermann (3-5, 2.82 ERA) looks to provide another solid outing, but earning personal victories has been much tougher for him than for Strasburg and Gonzalez.Zimmermann is one of only three major league pitchers -- along with Philadelphia's Cliff Lee and the Chicago Cubs' Ryan Dempster -- to possess a sub-.500 record while sporting an ERA less than 3.00. He allowed two runs in six innings of Washington's 7-6 win over the New York Mets on Tuesday, marking the third time this season he hasn't earned a decision when allowing two or fewer runs."It's no picnic facing Zimmermann or any of our starters," manager Davey Johnson said. "That's been our strength all year, holding the opposition down."He's 2-2 with a 1.55 ERA in eight lifetime interleague outings and was stellar in his only career start against the Red Sox, allowing one run in seven innings of a 9-3 win June 25, 2009.The Red Sox (29-30) have lost five of six at Fenway Park and five of six overall. They're in danger of being swept at home for the fourth time this season and the team's 18 home losses are already half as many as all of 2011.Boston hasn't been under .500 this late in a season since it was 78-79 on Oct. 3, 2001."The last two guys (Strasburg and Gonzalez) were pretty darn good," Dustin Pedroia, who is 2 for 20 over his last five games, told the team's official website. "We've got to come out and find a way to have better at-bats and score runs for our (pitcher)."Kevin Youkilis went 0 for 4 on Saturday, dropping him to 3 for 22 (.136) over his last six games for the Red Sox, who hope Jon Lester can get back on track.Lester (3-4, 4.64) has allowed at least four runs in his last four starts, going 1-1 with a 6.75 ERA in that stretch. He gave up four runs -- two earned -- over six innings of Boston's 8-6, 10-inning loss to Baltimore on Tuesday.The left-hander is 1-2 with a 6.42 ERA in six home starts, though he's won both of his career starts versus Washington with a 3.00 ERA, last facing the Nationals on the road June 24, 2009.With the return of Daisuke Matsuzaka, who took the loss Saturday, Boston designated outfielder Marlon Byrd for assignment.