Tucker finished with three field goals overall to back Joe Flacco's 355-yard passing performance as the Ravens (9-2) strengthened their hold on the AFC North with a fourth straight win.
Tucker booted the tying field goal on the last play of regulation after Ray Rice made a 29-yard catch-and-run on a fourth-and-29 situation with time running down.
Rice racked up 97 rushing yards on 22 carries, while also making eight grabs for 67 yards.
The Chargers (4-7) were led by Phillip Rivers, who completed 23-of-36 passes for 228 yards and a touchdown in his team's third consecutive loss.
Malcom Floyd caught a scoring pass among his four passes for 65 yards for San Diego.