(Sports Network) - Jon Lester attempts to bounce back from one of his worst starts of the season this afternoon, when the Boston Red Sox try to complete a three-game sweep of the New York Yankees in what will likely be the final game played between the bitter rivals at the current Yankee Stadium.

Lester lost for only the second time in his last 15 starts Saturday in Toronto, as the Blue Jays pounded him for seven runs and eight hits in just 2 1/3 frames. That dropped him to 12-5 on the year and raised his earned run average to 3.49.

The 24-year-old lefty has dominated the Yankees in two starts this season, winning both outings and allowing just two runs in 16 frames against them.

Boston delivered what very well could be the death knell to the Yankees' playoff chances on Wednesday, as Jason Bay finished 2-for-4 with four RBI and Dustin Pedroia added a grand slam in an 11-3 rout.

Jacoby Ellsbury collected two hits and scored twice for the Red Sox, who have won three in a row and four of five. Boston remained 3 1/2 games behind first- place Tampa Bay in the AL East after the Rays topped Toronto on Wednesday.

Kevin Youkilis, Alex Cora and Coco Crisp knocked in a run each for Boston. Paul Byrd (9-11) got the win after yielding five hits and two runs over six frames, with five strikeouts and a pair of walks.

Jason Giambi homered for the Yankees, who have lost two straight after a three-game sweep of the Baltimore Orioles and are now seven games back of the Red Sox in the wild card race. Alex Rodriguez and Robinson Cano also drove in a run.

Yankees starter Sidney Ponson (7-5) lasted only 4 2/3 innings, allowing seven hits and four runs with four walks in defeat.

New York will pin its hopes today on righty Mike Mussina, who is 16-7 with a 3.45 ERA. Mussina received a no-decision on Friday against Baltimore, as he allowed four runs and nine hits in six innings of a 9-4 win.

Mussina tossed six scoreless innings to defeat the Red Sox the last time he faced them and is 20-17 lifetime against them with a 3.74 ERA in 55 starts.

Boston has won eight of its 14 matchups with the Yankees this season.