The loss eliminated the Dodgers from the National League Western Division race and dropped them 3 1/2 games behind Florida for the wild card.
Gonzalez, who delivered the game-winning hit in Game Seven of the 2001 World Series, won't have a chance to play this October, but continued to torment the Dodgers. Of his 275 career homers, 29 have come against Los Angeles, his most against any opponent.
Webb (10-7), staked to a lead before taking the mound, became Arizona's second double-digit winner this season. He retired 14 of the final 15 batters he faced.
The losing pitched, 20-year-old righthander Edwin Jackson (1-1), was making his just second career start. Eight days after holding the Diamondbacks to four hits in six scoreless innings, he filled in for Odalis Perez and allowed two runs and five hits in seven frames.