Jason Bay returns to the Red Sox' dugout after homering in the second inning of Tuesday's game.

AP photo / Manuel Balce Caneta

WASHINGTON, D.C. -- The last time the Red Sox were in the nation's capital, they were celebrating their 2007 World Series championship with then-President George W. Bush at the White House.

Instead of roaming the Rose Garden and hobnobbing with political bigwigs, the Red Sox are in town on serious business this time. They made their first visit to the new Nationals Park Tuesday night . . . though any of the 41,517 in attendance could have closed their eyes and, judging by the crowd's reactions, thought they were sitting at Fenway Park. The ballpark was jazzed with a mix of Nationals fans and Red Sox fans, giving Washington its first sellout of the season. In fact, the 41,517 in attendance set a new record here.

And the Red Sox gave their followers among the 41,517 reason to celebrate, as they broke open a close game with seven runs in the final two innings and came away with a lopsided 11-3 victory.

"A lot of good things happened tonight," said manager Terry Francona. "[But] it took a while."

The victory lifted the Sox' A.L. East lead to five games over the New York Yankees, who lost Tuesday night in Atlanta. It's Boston's largest first-place lead since Sept. 15, 2007.

"As good as our record is, I kind of feel like we haven't really got hot yet," said Jason Bay. "We haven't got on one of those streaks. I don't think we've fired on all cylinders. With that being said, our record is pretty good and we're playing good baseball.

"I think it's scary that we can be even better," added Bay, who led the 17-hit attack by going 4-for-6, including a home run, three singles, three runs scored and three RBI.

"He's doing a heck of a job," said Francona.

Jacoby Ellsbury also had a big night, going 4-for-4 with a walk, three RBI and a pair of triples.

"I felt comfortable at the plate. I got some pitches I could drive and I took advantage of it tonight," said Ellsbury.

With a 4-3 lead heading into the top of the eighth, the Sox -- now 43-27, which is the best record in the American League and the second-best record in baseball -- exploded for six runs in the inning to silence the Nationals, who own the worst record in the majors (20-48) but entered Tuesday's game winners in four of their last five games.

"We had a lot of hits early on, but not a lot of runs," said Bay. "We got into their bullpen in that one inning and nobody wanted to make the last out. It's one of those games we haven't had in awhile."

On the heels of its current winning streak, Washington struck first.

With two outs in the bottom of the first inning, the Nats' Jordan Zimmerman reached on a single and Adam Dunn followed with a RBI double down the right-field line for a 1-0 advantage.

Boston responded in the top of the second as Bay homered to tie the score, crushing a 3-and-2 offering off Nationals starter John Lannan into the bleacher seats in left-center field. It was Bay's 19th homer of the season.

The Red Sox took the lead in the top of the fourth inning when Ellsbury provided a two-out triple, scoring Bay for a 2-1 lead. But the Nationals answered in the home half when they loaded the bases on starter Brad Penny (5 2/3 innings, 3 runs) and pushed the tying run across on a wild pitch.

The Red Sox kept the pressure on Lannan and regained the lead in the top of the fifth inning. Dustin Pedroia led off with a single to left -- his second hit of the game -- and reached second on a wild pitch. With one out, Youkilis drove the ball to left, scoring Pedroia to give Boston a 3-2 lead.

But a pair of former Red Sox helped the Nationals knot the game at 3-3 in the bottom of the sixth inning. Josh Bard lined a two-out single to right and scored when Willie Harris doubled to deep right field.

After the Nationals lifted Lannan with one out and nobody on in the seventh, the Red Sox were helped by a Washington miscue. Former Red Sox pitcher and current Nationals reliever Julian Tavarez got Youkilis to hit a ground ball to Ryan Zimmerman at third, but Zimmerman made a throwing error.

The play proved crucial.

Bay followed with a single to shallow left-center field and Youkilis had his sights on third base all the way. He reached safely and later scored on Varitek's sacrifice fly to give Boston the lead for good, 4-3.

"Awesome. Youk had his mind up right from the get-go he was going. There was no hesitation," said Bay. "Ultimately we tacked on a bunch of runs after that, but that sac fly put us ahead. It was a huge play and it was heads-up from him."

Bay collected two RBI with a bases-loaded single to left field in the top of the eighth inning for a 6-3 advantage. Varitek added a RBI single and Ellsbury collected his second triple of the game, driving in two more runs before Nick Green drove Ellsbury home for a 10-3 lead.

Just for good measure, the Sox added another run in the top of the ninth on a Youkilis RBI double.

jmcdonal@projo.com