Pittsburgh Pirates counterpart James McDonald has made significant contributions to his team as well.Zimmermann takes the hill opposite McDonald as the Nationals try for a two-game sweep of the visiting Pirates on Thursday night.Washington (23-14) has posted a major league-best 2.89 ERA thanks in large part to the early-season efforts of Zimmermann (2-3, 2.14 ERA), Stephen Strasburg and Gio Gonzalez. After failing to generate much offense against Gonzalez during Wednesday's 7-4 loss, the Pirates (17-20) could be in for another long night at the plate versus Zimmermann.The right-hander was superb again his last time out, yielding one run, five hits and striking out a season-high nine over seven innings of Saturday's 2-1 victory at Cincinnati."That's the best I've felt all year," said Zimmerman, who will make his first appearance versus the Pirates. "I had command of everything. My slider was really tight."Zimmermann has allowed one earned run in five of his seven outings this season. He is, however, receiving an average of just 2.14 runs of support -- one of the lowest marks in the majors.McDonald, meanwhile, seems to finally be coming into his own in his fifth big league campaign. The right-hander, who's gone 2-2 with a 2.42 ERA through his first seven starts, has fanned 33 in 29 innings over his last four.After posting back-to-back wins, McDonald suffered his second loss despite allowing just one run and four hits over a career high-tying eight innings Friday in a 1-0 defeat to Houston."It's fun to watch this young man take this step forward," manager Clint Hurdle said.In his only career start against Washington, McDonald gave up two runs in 6 1/3 frames but didn't factor in the decision of a 5-3 road victory last July 2.He'll look to slow down a Nationals team which has won five of seven games. The suddenly potent Nationals, who have scored at least six runs four times over that stretch, are 8-1 when scoring at least that many.Former Pirate Adam LaRoche shined brightest for the Nationals on Wednesday, belting his team-leading seventh homer before coming through with a three-run double for his 1,000th career hit."Always, in my opinion, Mr. Clutch," Gonzalez said.Batting .423 in his last seven games and .339 on the year, LaRoche is feeling no ill effects from the torn left labrum that cut his 2011 campaign short."I wanted to prove to myself that I could come back from this surgery and do what I know I'm capable of doing," he said. "To come out and do it is nice reassurance."LaRoche, who spent two-plus seasons with Pittsburgh from 2007-09, has gone 7 for 12 with three long balls and eight RBIs in four meetings versus his former team this season. The slugging first baseman is hitting .360 lifetime against the Pirates -- by far his highest career mark against any NL opponent.Josh Harrison provided most of Pittsburgh's offense Wednesday, hitting his first homer of the season and driving in a career high-tying three runs. The Pirates, though, have gone 12 straight games without scoring more than five runs."Some days you're going to feel good. Some days, you're not," Harrison said. "It's a matter of fighting through it."