Trailing 2-0 in the ninth, Philadelphia got doubles from Chase Utley and Delmon Young against closer Heath Bell, cutting the deficit to one run. Pinch-hitter John Mayberry followed with an RBI to forge a tie.
Then in the 10th, Jimmy Rollins collected a one-out single off Matt Reynolds (0-1) and Utley (4-for-5) followed with his second two-bagger, sending Rollins to third.
That brought up Howard, who sent a hit into shallow right field, sending home both runners as the Phillies earned a split in their four-game series.
The rally made a winner of Justin De Fratus (1-0), who got the final out in the bottom of the ninth. Jonathan Papelbon finished up with his seventh save.
Gerardo Parra socked a solo homer for Arizona.