DENVER -- At some point on their flight home from a lousy road trip, the Reds will likely be able to pick their dropped jaws off of the floor.

No one in a Cincinnati uniform could have fathomed any scenario where they lost a 6-5 game to the Rockies the way they did on Thursday. The sixth unanswered Colorado run came on a straight steal of home by pinch-runner Chris Nelson.

"It's one of those things you think will never happen, and it happened," said losing Reds reliever Nick Masset, who was on the mound when Nelson broke.

Some added salt to make this wound burn was the Reds blew a 5-0 lead built in the second inning. Their pitchers walked five batters, with four scoring. They tied a season high with five straight losses to finish a 1-6 road trip, and a Cardinals win in Atlanta reduced the Reds' division lead to five games. Meanwhile, the Rockies have won seven in a row.

"I don't think I've ever lost a game like that -- a steal at home," Reds manager Dusty Baker said. "They say if you've been around this game long enough, you see everything. When you're not going good, everything goes against you."

The Reds had a 5-4 lead in the eighth when the usually dependable Masset came on to pitch. An ugly turn of events set the wheels in motion for some heartbreak. Troy Tulowitzki led off the inning by muscling a 2-1 fastball very high and very away into the right-field seats for the game-tying homer.

"I don't even know how he hit it out," Masset said. "I thought it was high enough. I was trying to get him to chase."

Jason Giambi worked a walk and was replaced by Nelson. Melvin Mora followed with a hard grounder to first base. Joey Votto's toss to Masset covering the bag sailed over his head for an error that put runners on the corners.

With Miguel Olivo pinch-hitting, Nelson broke from third base before the first pitch.

"It was a squeeze play, but the pitcher wasn't really looking at me, so I just ran home," Nelson said. "I'm just running as hard as I possibly can run."

However, Masset spun toward second base thinking Mora was going to steal.

"I came set and they said, 'Step off.' My initial reaction was that the guy from first was going to second," Masset said. "I step off and turn around. By the time I looked at third base, that guy was halfway home and I didn't have a chance to get him."

By the time Masset turned again and threw home, Nelson had already slid headfirst across the plate. Catcher Ramon Hernandez didn't even have a chance to apply a tag.

Amazingly, that was the rookie Nelson's first career steal in the Majors. It was also the first time an opponent executed a straight steal of home against the Reds since the Padres' Eric Owens did it on May 21, 1999, at Qualcomm Stadium.

"It's embarrassing," said Masset, who hadn't given up a run in his previous 15 appearances. "It's something that shouldn't have happened. It's something I take complete fault for."

Nelson's daring is more stunning since Masset is a right-handed pitcher that was facing third base in the stretch position.

"That was a really risky play on their end that paid off," Votto said. "It worked for them today. I would say nine times out of 10, you're out at home."

Reds starter Travis Wood benefited from a 5-0 advantage early on, but saw his pitch count rise, which finished his day after five innings. A four-run top of the second inning included a two-run homer by Drew Stubbs off Jason Hammel. After that, Hammel retired 11 of the next 12 batters and got a double play to escape a jam in the sixth.

"We didn't score after the third. That was big," manager Dusty Baker said.

Wood issued two walks and saw both runners score. Following Tulowitzki's one-out walk in the fourth, Giambi boomed a two-run home run. Eric Young walked with two out in the fifth, and Wood paid when Dexter Fowler drove Young in with an RBI double.

Reliever Logan Ondrusek's seventh started with a walk to Ryan Spilborghs and Chris Iannetta's double. Rookie Aroldis Chapman put out the fire, but not before some tight moments. Pinch-hitter Jonathan Herrera hit a fielder's choice to first base, with Spilborghs scoring just ahead of Votto's throw to the plate. Chapman struck out Young for the first out, but walked Fowler to load the bases for Carlos Gonzalez, the NL's leading hitter.

On a 0-2 pitch, Chapman threw a 103-mph fastball to Gonzalez and induced an inning-ending 6-4-3 double play.

"That was a tough loss, especially after Chapman got out of that inning," Baker said.

Just as people started anointing the first-place Reds the likely National League Central champs, they have found ways to curb the enthusiasm with this road trip.

The loss was reminiscent of the punches to the stomach the Reds took in Atlanta and Philadelphia earlier this season. They responded with hot streaks both times.

"We're going to go through bad stretches during the season, and this is one of them," Votto said. "We just have to dig down a little deeper and look for tomorrow, be optimistic and plan on winning. We've done that several times this year."