Pittsburgh gave up Bay and wound up with four young players. The deal was completed just before the 4 p.m. Eastern time deadline for making trades without waivers.
The Dodgers began the day one game behind first-place Arizona in the NL West, and were seeking a big bat. Boston, in the middle of the AL East race and chasing a second straight World Series title, wanted a productive hitter in return and got that in Bay.
The last-place Pirates, looking for young talent, gave up their star outfielder and got reliever Craig Hansen and outfielder Brandon Moss from Boston and third baseman Andy LaRoche and pitcher Bryan Morris from the Dodgers.
LaRoche, Moss and Hansen will join Pittsburgh and Morris will go to Class A Hickory. Meanwhile, Ken Griffey Junior is back in a pennant race as he tries to reach the World Series for the first time in his stellar career.
The Chicago White Sox have acquired Griffey from the Cincinnati Reds. The White Sox are hoping the 38-year-old outfielder can help them hold onto their slim lead in the AL Central. Griffey has 608 career home runs and gives the White Sox left-handed power in their lineup.
The Reds sent Griffey and cash to Chicago for reliever Nick Masset and Triple-A second baseman Danny Richar. Masset was 1-and-0 with a 4.63 ERA in 32 games for Chicago. Richar was hitting .262 with nine homers for Triple-A Charlotte.