BOSTON(AP) The Yankees' best offensive game in more than two years began with another leadoff hit for Derek Jeter . It ended with four runs in the ninth inning.

Slugging from start to finish, New York beat the Boston Red Sox by a seemingly comfortable 20-11 margin on Friday night. But with the short Green Monster in left field and the Red Sox mounting comeback after comeback, the Yankees were relieved to take the opener of the three-game series.

''That was an uncomfortable 20 to whatever it was game,'' Jeter said, ''because you get a couple of guys on base (and) you pepper that wall and it could be a whole new game.''

Yankees manager Joe Girardi wasn't taking anything for granted, even after Hideki Matsui homered twice and drove in a career-high seven runs, Alex Rodriguez went 4 for 4 and Jeter went 3 for 6, actually lowering his batting average over an 11-game stretch to .543 (25 for 46). New York also led 12-1 after 4 1/2 innings.

But Jason Varitek and Mike Lowell homered in Boston's four-run ninth.

''When we ended the ninth,'' Girardi said, ''I felt pretty good.''

New York's 20 runs and 23 hits were its most since it had 21 runs and 25 hits against Tampa Bay on July 22, 2007. The 20 runs also were the most allowed by the Red Sox since the Yankees scored 22 on June 19, 2000, at Fenway Park.

This year, the Red Sox had won the first eight games between the rivals before the Yankees swept a four-game series at home from Aug. 6-9. None of that mattered Friday night.

''If you're carrying games that happen in April and May around and, what are we, in August right now, you're not going to be a very good team,'' Jeter said.

The Yankees' latest offensive outburst extended their winning streak to three and gave them a 7 1/2-game lead over Boston in the AL East.

The 31 runs were the most scored in a game between the two franchises, surpassing the New York Highlanders' 15-14 win over the Boston Americans on July 29, 1903, in Boston.

''They've got a lot of really good hitters over there,'' Girardi said. ''So you want to keep tacking on the runs.''

It helped that the Yankees were facing Brad Penny (7-8), who allowed eight runs and 10 hits in four-plus innings and is 1-6 in his last 11 starts.

''They have a great team,'' Penny said. ''One through nine, all can do damage. It's one of the better hitting teams you'll face in the league.''

New York has been rolling against all opponents with a 15-3 record in its last 18 games. Boston began a 10-game homestand after winning its previous three games in Toronto.

That momentum didn't last.

The Yankees scored two runs in the first inning, four in the second, six in the fifth, three in the sixth, one in the seventh and four in the ninth.

''It's plain and simple that we got our (butts) kicked pretty good,'' Lowell said.

Matsui hit three-run homers in the fifth and ninth, giving him 21 for the year, and drove in a run with a groundout in the seventh. He is batting .366 (15 for 41) with two homers and 10 RBIs against the Red Sox this season.

''We lost three games in a row twice here this season,'' Matsui said through a translator. ''In that sense, it was very important for us to set the tone.''

Rodriguez emerged from a 5-for-25 slump. Mark Teixeira and Melky Cabrera had three hits apiece and Teixeira drove in three runs. Jeter had his fourth three-hit performance in the last five games.

''He's probably as hot right now as I've ever seen him,'' Andy Pettitte said.

The Yankees led 12-1 before the Red Sox scored three in the bottom of the fifth off Pettitte (10-6).

Jeter doubled in the first, the fourth time in five games he led off a game with a hit. Teixeira walked, Rodriguez singled and Jorge Posada hit a two-run single.

There was one downside to the inning when Johnny Damon fouled a ball off his right knee, then struck out and left the game in the bottom half with a bruised knee. Girardi said he's day to day.

Eric Hinske , Damon's replacement in left field, doubled in a run in the second before a two-run double by Teixeira and an RBI single by Rodriguez.

Michael Bowden relieved Penny with two on in the fifth and Matsui hit his second pitch for his first homer. A run-scoring double by Robinson Cano and RBI singles by Cabrera and Teixeira made it 12-1.

The long inning may have affected Pettitte, who had allowed just one hit through four innings. In the fifth, Jacoby Ellsbury singled in two runs and Dustin Pedroia doubled in another. But the Yankees got those three runs right back in the sixth on Cabrera's run-scoring double and Jeter's two-run single.

NOTES: Ellsbury swiped a base to tie the Red Sox record of 54 steals set by Tommy Harper in 1973. ... The Yankees broke a seven-game losing streak at Fenway Park. ... New York activated LHP Damaso Marte from the 60-day disabled list and optioned 3B Ramiro Pena to Triple-A Scranton-Wilkes Barre. ... The Red Sox activated Rocco Baldelli from the disabled list, called up Bowden from Triple-A Pawtucket, optioned OF Brian Anderson to Pawtucket and designated RHP Fernando Cabrera for assignment. ... New York's Nick Swisher reached for the 29th straight game, the longest current streak in the majors.