Chicago moved within one game of the first-place Houston Astros in the National League Central and moved within 2 1/2 of the Florida Marlins for the wild card. Prior has eight of the 20 wins recorded by Chicago starters since the start of August.
Prior (16-6) gave up just two runs and six hits while walking one. The 23-year-old righthander was denied a chance at his fourth complete game of the season after allowing an RBI double to Matt Watson with two outs in the ninth..
It was the 534th career home run for Sosa, who tied Hall of Famer Jimmie Foxx for 11th place all time. Sosa reached 35 homers for the ninth consecutive season.