Jason Bay drove in four runs, Dustin Pedroia hit a grand slam and the Boston Red Sox routed the listless Yankees 11-3 on last night, putting an emphatic dent in New York’s dwindling playoff chances.

Paul Byrd beat the Yankees in a crucial game for the second consecutive year, and David Ortiz reached base four times for the second straight night.

Pedroia’s first career slam capped a seven-run eighth inning and sent hordes of booing Yankees fans shuffling toward the exits. With co-chairman Hank Steinbrenner in attendance, New York dropped seven games behind Boston, which leads the AL wild-card race by 2.5 games over Minnesota.

The Red Sox remained 3.5 games behind first-place Tampa Bay in the AL East.

In a game they needed badly, the injury-depleted Yankees gave the ball to Sidney Ponson (7-5). He lasted 4.2 innings and dropped to 3-13 with a 6.95 ERA in 22 starts against the Red Sox.

Boston will try for a three-game sweep Thursday with lefty Jon Lester on the mound against 16-game winner Mike Mussina.

Byrd (9-11) stymied New York’s struggling hitters with floaters and soft stuff, just as he did last October when the right-hander won at Yankee Stadium to clinch a first-round playoff series for Cleveland.

Still using his old-fashioned windup, Byrd allowed two runs and five hits in six innings. He struck out five and improved to 2-1 in three starts since Boston acquired him from the Indians this month.

Byrd has won six of his last seven starts following a five-game losing streak.

Also a Red Sox newcomer, Bay hit a two-run double in the first and an RBI triple in the eighth when Boston battered relievers Jose Veras and David Robertson.