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DENVER -- Chris Nelson was watching when Nick Masset looked down at the ground.

Talk about a heads-up play.

Nelson stole home in the eighth inning to send the Colorado Rockies to a 6-5 victory over the Cincinnati Reds on Thursday, completing a four-game series sweep and extending their winning streak to season-best seven games.

With one out and runners on the corners, Nelson broke for home before Masset (3-4) threw his first pitch to Miguel Olivo. Inexplicably, Masset stepped off the mound, whirled to his left and toward second base.

"He was just looking right at the ground," Nelson said. "He wasn't paying me any attention. [Third baseman Scott] Rolen was playing back. So I just decided I should just go ahead and go. I didn't stop."

Nelson scored easily to give the Rockies a 6-5 lead. He became the first player to take home for his first career steal since Dan Uggla of the Florida Marlins accomplished the feat on April 21, 2006, against the Philadelphia Phillies, according to STATS LLC.

The Rockies, who trailed 5-0 after two innings, had called for a suicide squeeze but it never got that far.

"Once I made up my mind I was going, I was going," Nelson said.

Masset, who had made 15 consecutive scoreless appearances, said he came set, stepped off the mound and initially thought Melvin Mora was going to second.

"I turned around and by the time I looked to third base the guys was halfway home and I didn't have a chance to get him," Masset said. "It was a complete mistake on my part. You should check the runner at third right away and go from that. I passed that because normally you get the guy at first who is trying to be sneaky. It was a complete mishap on my part. It is embarrassing, something that should never have happened, just something you never see before."

Nelson said he had never stolen home in any game, at any level, before Thursday. When he got back to the dugout, a lot of players were asking how he did that.

Nelson was the Rockies' first-round pick in 2004 but is in his first stint in the majors.

Reds manager Dusty Baker said he had never lost a game in this fashion. Cincinnati has dropped five straight overall and its lead in the NL Central was trimmed to five games when the St. Louis Cardinals won 11-4 at Atlanta on Thursday night.

Troy Tulowitzki started the winning rally with a leadoff drive off Masset for his 18th homer and sixth in the past seven games.

"It was a fastball up," Tulowitzki said. "I'm a good fastball hitter. I got on top of it, and it went out."

Jason Giambi, who hit a two-run homer in the fourth, followed with a walk and was replaced by Nelson. First baseman Joey Votto, in the running for NL MVP, then made a critical error on Mora's slow bouncer. He charged the grounder, but his underhand flip to Masset covering first was high and wide.

Nelson went to third on the play, setting up the 15th swipe of home in Rockies history and first since Matt Holliday in 2006. It was the first straight steal of home against the Reds since Eric Owens of the Padres did it May 21, 1999, at San Diego.

Huston Street allowed a leadoff single to Ramon Hernandez in the ninth and then struck out the side for his 17th save in 21 save opportunities.

The Rockies have won 10 straight games against the Reds at Coors Field and 19 of their past 22 games overall against Cincinnati.

Matt Belisle (7-5) recorded two outs in the eighth to get the victory.

Cincinnati got off to a nice start against Jason Hammel, who pitched seven innings.

Brandon Phillips singled, stole second and advanced to third on a wild pitch before scoring on Votto's swinging bunt in the first.

The Reds added four more in the second. Hernandez hit an RBI double and scored on Paul Janish's single. After Travis Wood sacrificed, Drew Stubbs hit his 16th homer and first since Aug. 14.

Hammel then settled down and pitched five scoreless innings, allowing three hits in that span.

"After that second, I just got to dig deep and battle and find a way to get deep in the game," Hammel said. "I'm proud of it."

Giambi's fifth homer started the comeback. Dexter Fowler added an RBI double in the fifth and pinch-hitter Jonathan Herrera drove in a run with a grounder in the seventh, making it 5-4.

Colorado had a chance to move in front in the seventh but left-hander Aroldis Chapman got MVP candidate Carlos Gonzalez to ground into an inning-ending double play with the bases loaded. Gonzalez grounded a 103 mph fastball right to shortstop Janish.

At 76-64, the Rockies are a season-best 12 games above .500. They have won 14 of their past 16 games and are 47-22 (.681) at Coors Field.

With an eye toward the postseason, Baker said, "The way they're playing, there is a good chance we'll come back and play them again."

If so, Nelson's steal of home will be remembered as a key part of Colorado's resurgence. It helped the Rockies complete their 23rd comeback victory this season.

"Gutsy thing that he did and it worked out," Tulowitzki said. "Sometimes those things don't work out and you don't look very smart."

Game notes

Toronto claimed reliever Taylor Buchholz, whom the Rockies designated for assignment Tuesday. ... Rockies left-hander Jeff Francis will start Monday against the Padres in place of injured Aaron Cook. ... Reds shortstop Orlando Cabrera was given the day off as a precaution after playing three games following a month on the disabled list with a strained left oblique muscle. ... Reds outfielder Jay Bruce (right side strain) took batting practice, but Baker said Bruce was not ready to play yet. ... Rockies first baseman Todd Helton, who has one hit in his past 22 at-bats, was given a planned day off following a night game.

Information from ESPN The Magazine's Buster Olney and The Associated Press was used in this report.

Copyright by STATS LLC and The Associated Press