Maddux, who was traded from San Diego on Tuesday, allowed seven runs and nine hits in 5 2-3 innings, one of his worst outings of the season. The right-hander remained stuck on 353 wins, one shy of tying Roger Clemens for eighth on the career list.
Howard was a big reason why, hitting an opposite-field shot for his 34th home run and giving the Phillies a 2-1 lead in the fourth inning. Howard had entered the at-bat 3-for-36 with 18 strikeouts and just one homer in his last 14 games.
The Phillies did most of their damage in the sixth inning, when they scored four runs and knocked Maddux (6-10) out of the game. Coste capped the frame with a three-run homer to left field as the Phillies' slumbering offense scored its most runs this month.
Philadelphia entered Friday night with 61 runs in its 19 games (3.1 per contest), and hadn't scored more than seven runs since July 31.
Kyle Kendrick (11-7) rebounded from two poor outings and a first-inning homer by Andre Ethier, going 5 2-3 innings and giving up only two other hits while striking out three and walking one. Kendrick had allowed 13 runs on 15 hits in seven innings his last two outings, including an 8-6 loss against the Dodgers on Aug. 11 in Los Angeles.
Maddux, who was 6-3 with a 3.30 ERA in 12 starts in his first stint with the Dodgers in 2006, allowed more than nine hits only three times in 26 starts with the Padres this season.