Todd Helton hit a two-run homer off closer J.J. Putz in the bottom of the ninth inning and the Colorado Rockies rallied for an 8-7 win over the Arizona Diamondbacks on a rain-soaked Saturday night.

With two outs, Helton belted his first homer of the season down the right-field line and the towering shot stayed just fair. He raised his hands in the air as he rounded the bases and was mobbed by teammates at home plate.

Tyler Chatwood (1-0) pitched two innings and gave up a run to earn the win in relief.

The Diamondbacks were trailing 5-1 when the game was halted by a relentless downpour after four innings. But the 71-minute break energized their bats and they came out of the clubhouse swinging.

Miguel Montero hit a three-run homer and pinch-hitter Paul Goldschmidt broke a tie with a sacrifice fly in the seventh.

The lead wouldn't last as Putz blew his first save of the season. He hit Marco Scutaro with a pitch to start the ninth inning, but got pinch-hitter Jason Giambi to pop up and then struck out Troy Tulowitzki.

That set the stage for Helton, who also delivered what turned out to be the game-winning hit the night before with a double in the eighth.

On this dreary night in the Mile High City, the grounds crew kept shoveling layers of diamond dust on the soaked infield to dry it out, but that hardly helped. The persistent rain made every play an adventure.

So slick was the field that smooth-fielding shortstop Tulowitzki had two throwing errors — in one inning.

Later, left fielder Gerardo Parra slipped while chasing down an RBI double by Eric Young Jr., which made it a 7-6 game.

Goldschmidt had a big at-bat off the bench with Chris Young standing on third. He hit a high fly to right off Rex Brothers that Michael Cuddyer had plenty of time to camp under.

His throw was on line, too, but Young slid around the tag of catcher Ramon Hernandez.

The Diamondbacks added an insurance run in the eighth when Ryan Roberts put down a squeeze bunt and John McDonald avoided the tag of Hernandez. McDonald also drove in the tying run in the seventh on an RBI double that scored Aaron Hill, who reached on Tulowitzki's error.

All this after hard-luck starter Jhoulys Chacin departed.

These days, Chacin can't win even when the hard-throwing righty is, well, winning.

He was rolling along in the drizzle as he methodically set down the Diamondbacks with a more aggressive approach on the mound. But just as he was about to duck out of the dugout for the fifth inning, the umpires signaled for the tarp.

With that, his night was finished.

Chacin had his good stuff, too, the kind of movement on his pitches that has led manager Jim Tracy to proclaim him an ace in the making. He scattered four hits and gave up one run over four innings, but is still searching for his first win since Aug. 28.

It was definitely a step in the right direction.

He pledged to be more aggressive against the Diamondbacks, instead of nibbling at the plate as he did in his season debut.

Chacin did just that, too, throwing 41 of his 64 pitches for strikes.

He also helped himself at the plate, driving in a run on a grounder off counterpart Josh Collmenter, who was let off the hook for a second straight outing.

Collmenter gave up six runs — five earned — in three innings against the Giants, only to see his team rally back in that contest.

The speed of Dexter Fowler led to a run in the third. With two outs and Fowler on second, Cuddyer hit a slow roller to first baseman Lyle Overbay, who flipped the ball to Collmenter with the pitcher racing toward the bag.

Only, it wasn't in time and Fowler, hustling the entire way, darted for home, sliding under the tag of Montero.

On this damp and cool evening, Collmenter's cutter did anything but cut, especially in the second inning as the Rockies hit back-to-back homers. Tyler Colvin lined the pitch over the fence in right for a two-run homer.

Four pitches later, Hernandez crushed another Collmenter cutter for a solo shot to straightaway center.

Colvin received the start in left with Carlos Gonzalez taking a sick day due to strep throat.

NOTES: The start was delayed 16 minutes by a steady rain. ... Before the game, the Rockies reinstated Charlie Blackmon (turf toe) from the 15-day disabled list and optioned the outfielder to Triple-A Colorado Springs.