Trailing 3-1 entering the sixth inning, Howard bashed a three-run homer off Kyle Lohse (0-1) and, after a Shane Victorino single, Ibanez unloaded a two-run shot for the the National League East champion Phillies.
Howard finished with four RBI and Victorino went 3-for-5 with two runs batted in for the Phillies, who went only 3-6 against St. Louis in the regular season.
Roy Halladay (1-0), who threw a no-hitter in last year's Game 1 of the NLDS, didn't equal that feat this time, but did settle down after a rough beginning to claim the victory.
The Phillies ace went allowed three runs on three hits over eight frames, walking one and striking out eight.
Lance Berkman hit a three-run homer for NL wild card champs St. Louis.
Lohse ended up allowing six runs (five earned) on seven hits in a 5 1/3-inning effort.