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PHOENIX -- Strong pitching is supposed to make the Arizona Diamondbacks a contender. Big bats made them a winner on Opening Day.

Tony Clark and Arizona newcomer Felipe Lopez each homered from both sides of the plate as the Diamondbacks outslugged the Colorado Rockies 9-8 on Monday.

Eight home runs were hit in the game, including the decisive shot by Chad Tracy leading off the seventh inning against reliever Jason Grilli (0-1).

"It was a heavyweight fight out there. It was blow after blow," Tracy said. "Every time we scored, they scored, and we finally had the last say."

Lopez and Clark became the first switch-hitting teammates to homer from both sides of the plate in a game since Jorge Posada and Bernie Williams did it for the New York Yankees on April 23, 2000. It had never been done on Opening Day.

"Pretty amazing," Diamondbacks manager Bob Melvin said. "Pretty phenomenal."

Lopez, signed as a free agent in the offseason, is the first Arizona player to homer twice in his first game with the team. He is the first to do it in the majors since Richie Sexson for Seattle on April 4, 2005.

Troy Tulowitzki, Chris Iannetta and Seth Smith hit solo homers for the Rockies.

Arizona ace Brandon Webb was rocked for six runs and six hits in four innings. Rockies starter Aaron Cook fared even worse, allowing six runs and seven hits in 2 1/3 innings. Neither had command of their featured pitch, the sinker.

"I was up in the zone," Cook said. "The sinker was flat and you saw what happened, just not a normal day for me and Webby, either."

Webb said he was dropping his arm too low and was bothered by stiffness in his shoulder early in the fourth inning, when he gave up consecutive homers on three pitches to Tulowitzki and Iannetta. He said he felt fine after the game, though.

Tony Pena (1-0) worked 1 1/3 scoreless innings for the win and closer Chad Qualls got three outs for a save.

"If they hit five home runs, you're in a bad place. You're struggling," Colorado manager Clint Hurdle said of his pitchers' woes. "I'm real proud of the way our offense battled back."

Tracy, who says he's finally healthy after a long recovery from major knee surgery, was 3-for-4 with two RBIs and two runs scored for Arizona.

"I came straight off the training table to playing last year," Tracy said. "This year I got to get in there and get some strength in my legs. So we'll see how things play out. This is one out of 162 so we've got a long way."

Colorado's Brad Hawpe was 3-for-4 with two doubles and three RBIs.

Hawpe lived up to his reputation as one of the toughest hitters against Webb, going 2-for-2 with a three-run double against the Arizona ace. That improved his career average against the 2006 NL Cy Young Award winner to .367 with 16 RBIs in 49 at-bats. Nine of his 18 hits have gone for extra bases.

"I look for a strike. I look for something to hit," Hawpe said. "He's obviously one of the best pitchers in baseball. I try not to think too much and just look for something to hit."

Colorado scored four times in the third to go up 4-2, but Arizona came back with four in the third off Cook to take a 4-2 lead. Tracy singled in a run, Eric Byrnes drove in another with a sacrifice fly and then Clark hit a two-run shot to right to put the Diamondbacks ahead 6-4.

Webb, a 22-game winner last season, couldn't hold the lead. Tulowitzki and Iannetta hit consecutive solo homers on three pitches to tie it at 6.

Lopez led off the game with a homer.

"I guess I set the tone," he said, "for both teams."

He added another, off reliever Glendon Rusch, to put Arizona back on top 7-6 in the fourth. Colorado tied it in the eighth on Hawpe's double and an RBI single by Ian Stewart.

Clark's 442-foot home run to straightaway center off Rusch in the fifth regained the lead for the Diamondbacks, 8-7. Colorado tied it again with Smith's homer leading off the seventh.

"They kept throwing punches," Clark said. "We were fortunate to punch back."

Game notes

Clark had three homers last season. ... Colorado was 3-15 against Arizona last season. ... Webb is 1-0 with three no-decisions in Opening Day starts. ... The Diamondbacks play 18 of their first 21 games at home. ... Colorado's roster includes 17 players 29 or younger, eight of them no older than 25. ... The crowd was announced as 48,799 and a sellout but there were many empty seats.