The Florida Marlins were one strike from a much-needed victory Monday night. Instead, they lost for the 10th time in 11 games, falling 7-4 to the Colorado Rockies when Jason Giambi hit a walk-off three-run homer after a poor defensive play gave Dexer Fowler a double and the Rockies unexpected life.

Giambi drove a 1-2 pitch from Randy Choate into the stands in right field to give the Rockies their first walk-off win this season. They had been 0-55 when trailing after eight complete innings, including 0-25 at home.

Giambi came off the disabled list on Friday and played for the first time since he strained his left quadriceps muscle on July 25.

"I hung a pitch," Choate said of the slider he threw Giambi, who had been hitless in four previous at-bats against him. "I've had success against him in my career. I don't think I did anything different. It's part of playing here. I'm not going to blame it on the air. I just hung it out over the plate. I think he was sitting on the pitch. He just took a pitch that was up and hit it out."

Marlins closer Leo Nunez (1-3), got the last out of the eighth when he struck out pinch-hitter Ty Wigginton with runners on first and second. Wigginton is 7 for 52 with two outs and runners in scoring position. Nunez then retired the first two batters he faced in the ninth before Fowler blooped Nunez's 3-2 pitch into short center field. Three Marlins converged on the ball, but it fell for a hit.

The speedy Fowler took a sweeping turn around first base. He was halfway to second and appeared to be caught for the third out when third baseman Greg Dobbs, who was covering second, took a throw from second baseman Alfredo Amezaga. Dobbs wheeled and threw to first base to get the retreating Fowler, who suddenly stopped going back to first. Dobbs' throw was wide, enabling Fowler to reach second with a double.

"Looked like they wanted to give it to us, and we didn't want to take it," said Marlins manager Jack McKeon, who managed his 2,000th game in the major leagues.

Asked what he thought when Amezaga threw the ball to second base with Fowler well on his way there, McKeon said, "'This is perfect. We got it.'"

That wasn't the case, and Carlos Gonzalez lined a double to right to score Fowler and tie the game. Nunez intentionally walked Troy Tulowitzki, whose two-run homer in the third off starter Clay Hensley had given the Rockies a 3-2 lead, and Giambi hit his 11th home run in 101 at-bats this season and the seventh walk-off homer of his career.

The Marlins had taken a 2-0 lead in the first on Mike Stanton's 27th home run, a drive off starter Kevin Millwood that landed on the concourse in center field. Millwood, who pitched six innings in his second start for the Rockies, gave up a two-run homer to John Buck in the fourth that gave the Marlins a 4-3 lead they held until Fowler's scamper kept the ninth inning alive for the Rockies.

As Fowler's hit fell between Amezaga, shortstop Emilio Bonifacio and center fielder Dewayne Wise, Amezaga scrambled to get the ball and threw to Dobbs, who went to cover second base.

"Second base is vacated," Dobbs said. "I'm sure (Fowler) was seeing that. I'm sure (Glenallen) Hill, their first base coach, was telling him to take an aggressive turn, make somebody get there. It's my job to get there in that situation. That's not a surprising play. We work on that. That's why I was on second base before the throw.

"What surprised me was when I got the throw, I didn't see (Fowler) stop and turn around because I was focused on getting the throw. When I turned to throw, out of the corner of my eye (I saw) he was running (back) to first but then he stopped and turned like three quarters of the way to first base as I'm in the motion of throwing. It threw me off. In retrospect, I should have just held the ball and ran at him. But I was thinking he was trying to get back to first. That's my instinct."

Rex Brothers and Matt Belisle (7-4) combined to hold the Marlins scoreless for the final three innings.

After going 1-9 on a homestand that ended Sunday, the Marlins began a seven-game trip. They are better on the road (31-24) than at home (25-41) but any hopes of ending their tailspin with a one-run win Monday dissolved into a bitter, unexpected defeat.

"It was one of those nights," McKeon said.

Notes: McKeon, 80, has a record of 1,035-965 in the majors. ... Rockies third base coach Rich Dauer resumed his duties. He suffered a broken nose when struck with a thrown ball during batting practice before Sunday's game at St. Louis. ... In 11 games, including five starts, at Coors Field, Hensley is 2-1 with a 2.65 ERA (37 1-3 innings, 11 earned runs). He allowed three runs in 5 2-3 innings with a season-high five strikeouts. ... Marlins reliever Edwin Mujica, who pitched 1 1-3 innings, left with a right lat strain after retiring Giambi on a pop fly in the eighth. ... Buck's 14 homers are the most by a Marlins catcher since Miguel Olivo hit 15 in 2007.