PITTSBURGH -- Pedro Alvarez could only envision one way in which the most dramatic moment of his burgeoning baseball career can be topped.
"It's pretty unreal," the rookie said. "I can remember one other time hitting a walk-off home run, but obviously here on a Saturday night, a packed house, in the big leagues, nothing can beat that -- maybe expect Game 7 of the World Series."
Alvarez's 10th homer in 45 career games -- and second in as many days -- came on an 0-1 pitch from Huston Street (2-3) with Andrew McCutchen and Garrett Jones aboard, allowing the seventh sellout crowd at PNC Park this year to enjoy a post-game George Thorogood concert all the more.
"This was a great win in front of a big crowd," Pirates manager John Russell said. "The guys were excited. I think the baseball gods are finally looking down on us saying, 'Enough is enough.' We did a lot of great things tonight, and unfortunately we were in a position to lose it."
Jones and Chris Snyder also homered for last-place Pittsburgh, which has won three of five. Alvarez, the No. 2 overall draft pick two years ago, connected for the ninth time at home this season, capping a 3-for-6 night.
"For a young guy to come up in those big situations like that, that's huge," Snyder said. "That's how you set the tone of a solid career."
The 36-year-old Helton, a former National League RBI champion, homered for only the third time this season, a line drive deep into the elevated seats in right after Dexter Fowler led off the inning with an infield single.
The first baseman had one of the best views of Alvarez's winner down the line.
"I wasn't sure it was a home run when he hit it," first baseman Helton said. "But based on the way he reacted, I figured he knew."
The Rockies have lost eight of their last nine on the road, making it difficult for them to remain in the NL playoff race.
"It's a tough loss, obviously," Rockies manager Jim Tracy said. "We haven't done that all year, to come back like that and then lose, it's tough."
Stewart's 16th homer was to right-center off Joel Hanrahan after Troy Tulowitzki and Brad Hawpe singled to lead off the ninth. Hard-luck Pirates starter Ross Ohlendorf was in line for his second win before Hanrahan's first blown save opportunity since he inherited the closer's job when Octavio Dotel was traded at the deadline last Saturday.
Stewart's drive was his fifth since the All-Star break and eighth coming in the seventh inning or later.
Pittsburgh trailed 1-0 before Snyder hit a three-run homer high off the left-field foul pole off Jorge De La Rosa in the sixth. It was Snyder's 11th homer and first since being acquired from Arizona.
Ohlendorf took line drives off his body early during each of his two most recent starts -- including one off his head in Colorado on July 28 that forced him to leave the game in the first inning. He made it through Saturday unscathed, allowing two runs, one earned, and four hits in six-plus innings.
Colorado got an unearned run in the seventh, but Jones got that right back when he led off the bottom half with his 16th homer and fourth in six games against the Rockies this season.
Still, the Pirates were more impressed with Jones' at bat in 10th, in which he worked an eight-pitch walk.
"He could have been selfish and tried to go for the fences," Alvarez said, "but he tried to put together a good at bat, which he did, walked and gave the opportunity to the next guy."
An opportunity Alvarez took advantage of.
"He's one of those guys who really wants to be on the stage -- in a good way; not in a cocky way," Russell said. "He wants to be the guy."
RHP Esmil Rogers will start for the Rockies on Sunday. Rogers is 1-2 with a 4.85 ERA in 13 games, two starts, this season. The rotation turn came available when the team placed RHP Aaron Cook on the disabled list Thursday. ... Every Pittsburgh starter had at least one hit -- including the 6-foot-4, 245-pound Ohlendorf managing an infield single. ... The Rockies used every available pitcher in their bullpen.