But in the seventh inning, when Willie Harris blasted a two-run home run high in the rightfield stands, giving Washington an eight-run bulge, there was no more trepidation. As Harris circled the bases, the Nats piped Chuck Brown’s “Bustin Loose” over the loudspeaker.

Whether it was hip-hop music or clutch hitting, the Nationals timing was uncharacteristically on-point Thursday night in a 9-3 victory before a sellout crowd of 41,985, which established a new Nationals Park record for the third straight night.

“With that lineup, you’re never relaxed anyway,” said Nats manager Manny Acta of the Red Sox, who scored a combined 17 runs the previous two nights. “But Willie Harris had that huge hit and that let us relax a little bit.”

Also helping calm Acta’s nerves was rookie right-hander Jordan Zimmermann, who had the best start of his career, matching his high for innings pitching (7) and his low for runs surrendered (1), holding the Red Sox to a harmless five singles in notching his first win in two months.

“It’s nice to get a W today instead of an L or a no-decision,” said Zimmermann. “I can’t give enough credit to my defense. [Ryan Zimmerman] had maybe two-three web gems over at third.”

Jordan Zimmermann, 23, was two-year-old when the man he beat Thursday, Boston right-hander John Smoltz, made his big league debut. Smoltz, pitching in the majors for the first time in more than a year following shoulder surgery, showed his rust in the first inning, surrendering four runs, before settling down and fanning the side in his final inning, the fifth.

“He had a little bump in the road in the first inning, but after that he did good,” said Jordan Zimmermann. “It’s definitely cool to go out and do that. I had a chance against [the Giants] Randy Johnson, came up a little short, now Smoltz.”

Zimmermann retired the opening batter in all but one inning, shutting down Boston leadoff man Dustin Pedroia, who went 0-for-4 with two strikeouts, and clean-up batter David Ortiz, who went hitless in three trips.

“He threw the ball well, pitched a great game,” said Smoltz, 42. “He’s why they won.”

The Nats (21-49) gave Zimmermann breathing room with their early binge, the most runs they’ve scored in the opening inning since Apr. 18. It started when Smoltz plunked Nick Johnson in the shin. After Ryan Zimmerman doubled down the leftfield line, Smoltz walked Adam Dunn to load the bases. Josh Willingham and Josh Bard followed with run-scoring singles and Anderson Hernandez finished off the rally with a two-run single.

With a big lead, Jordan Zimmermann (3-3) was free to challenge the Red Sox hitters. The lone run for Boston (44-28) came when J.D. Drew and Jason Bay hit look-alive singles to the same spot in left-centerfield, followed by a sacrifice fly by Ortiz. After that, however, Zimmermann resumed command.

“He’s not intimidated. He attacks hitters with his best stuff, his fastball, regardless of who we’re playing,” said Acta. “I think the kid has a chance to be a top of the rotation guy for years to come.”

Notes » Nick Johnson left the game after he was hit on the shin with a pitch in the first inning. After laboring around the bases, Johnson was removed from the lineup, Dunn coming in from the outfield to play first base. “Nick had a lot of swelling in his leg. It has lowered some,” said Acta after the game. “We’re gonna wait overnight and we’ll evaluate tomorrow when we get to Baltimore.” … Tyler Clippard pitched the final two innings for the Nats, giving up a two-run home run to late-inning replacement Rocco Baldelli.