It was his defense, however, that kept them in position to win.
Two innings later, with two outs, Werth hit a mammoth drive to center off Juan Gutierrez (0-2).
"He's as five-tool as it gets," said Arizona's Kelly Johnson, who provided all of his team's offense with a two-run homer in the fifth. "Everybody knows it now. It took a couple years of doing that before anybody finally said, `This guy's kind of good.' ... He can do a little bit of everything."
Philadelphia's home runs spoiled Ian Kennedy's best outing of the season and prevented Arizona from winning consecutive games for the second time this year.
Ibanez tied it at 2 with a solo shot with two outs in the seventh inning, one of the few pitches Kennedy said he wished he had back.
"It was not as located as I wanted," he said. "I felt like it was the right pitch. It just hung a little bit."
It was Ibanez's first home run of the season after hitting a career-high 34 last year.
Kennedy, who hadn't gone past five innings in any of his first three starts this season, retired the Phillies in order in five of the first six innings and set down 15 straight during one stretch.
Looking for his second major league win and first with Arizona, the right-hander allowed two runs on four hits and struck out four in a career-high eight innings.
"Ian was exceptional," Diamondbacks manager A.J. Hinch said. "I loved his aggressiveness. I thought he pounded the zone early and often and was able to locate all his pitches."
Acquired from the Yankees as part of a three-team offseason trade that also brought Edwin Jackson to Arizona and sent Curtis Granderson from Detroit to New York, Kennedy had Phillies batters swinging ahead of his off-speed pitches most of the game. But they timed two perfectly.
Werth's homer in the second inning put the Phillies up 1-0 and was Philadelphia's first in 46 innings, ending the team's longest stretch without a long ball since 2006.
Werth has eight multihomer games in his career -- and in his last six games against Arizona he is 11 for 24 with six home runs and eight RBIs.
"Today was just one of those days where I got the ball up in the air a little bit, and it happened to be a good day," said Werth, who has reached base in all 17 games he has played this season.
Phillies manager Charlie Manuel was much more excited about his right fielder's performance.
"Werth had a great game," Manuel said. "He made a tremendous catch out in right-center and the two home runs, he crushed them both. I would have paid to see those."
Johnson hit his third home run in two games to give Arizona a 2-1 advantage, but the Diamondbacks had only three hits after the fifth inning.
Nelson Figueroa, who made a spot start in place of injured J.A. Happ, allowed two runs and five hits in five innings for Philadelphia. He left the game with mild left hamstring soreness after throwing 100 pitches.
"Before the game we thought if he'd go 60 or 70 pitches that would be tremendous," Manuel said. "He did a heck of a job."
Figueroa's last start for Philadelphia was Aug. 31, 2001. The last pitcher to go at least eight seasons between starts for one team was Carlos Pulido for Minnesota: Aug. 7, 1994, and Sept. 9, 2003. ... Johnson has reached base safely in 15 consecutive games and has six home runs this season after hitting eight in 108 games with Atlanta last year. ... Kennedy's previous career high for innings pitched was seven on Sept. 13, 2007, for the Yankees at Toronto.