The marathon game was the longest in the majors this season.
Hundley had two of the Padres' hits, the biggest one off Micah Owings (3-4) with a home run over the wall in left field, giving San Diego consecutive victories for the first time since April 16-18.
Edgar Gonzalez and Brian Giles each had solo home runs for the Padres, who have lost 19 of 25 since starting the season 9-3. Jody Gerut had two RBI, while Josh Geer was tagged for five runs on five hits with two walks and two strikeouts.
Laynce Nix and Jay Bruce each hit two-run homers for the Reds, while Ramon Hernandez finished with a pair of hits.
Luis Perdomo (1-0), San Diego's eighth pitcher, didn't allow a hit over the final three innings and picked up the victory in his first major league decision.