The Reds had an 8-0 lead going into the sixth inning and saw the last of that advantage evaporate in the ninth when Jon Jay hit a solo homer that forced extra innings.
One of the runs during the St. Louis rally was driven in by Albert Pujols, who returned from the disabled list a month earlier than expected. Pujols, who suffered a broken wrist June 19, went 1-for-6 with one RBI in his comeback game.
Bruce walked to open the 13th against Raul Valdes (0-1), who was making his fourth appearance of the season. Bruce moved to second on a one-out single by Drew Stubbs and scored the game-winner on the two-out double by Hernandez.
Jose Arredondo (1-3) worked the 11th and 12th innings to get the win. Aroldis Chapman worked around a one-out single in the bottom of the 13th to claim his first save.
Chris Heisey, Bruce, Fred Lewis and Scott Rolen all homered over the first five innings to account for six Cincinnati runs.
The St. Louis rally was highlighted by a five-run seventh that included the RBI single from Pujols and a solo homer by Matt Holliday.