Jason Giambi homered twice and drove in five runs, hitting a solo shot to lead off the 10th inning on Sunday night and giving the Yankees an 8-5 victory over the Red Sox that extended their lead in the AL East to a season-high 5? games. Jorge Posada also homered in the 10th for the Yankees, who have beaten Boston in four straight this weekend and eight of the last nine. A victory on Monday would give New York a five-game sweep and a repeat of the 1978 "Boston Massacre," a four-game September sweep by a combined score of 42-9 that erased the remnants of Boston's 14-game lead in the division.