With the two-game sweep, the Rockies, who also got a solo homer from Troy Tulowitzki, moved a half game ahead of San Francisco in the division, and they snapped a streak of nine straight losses in games started by ace Ubaldo Jimenez.
Although he's still searching for his first win since Sept. 17, Jimenez showed signs of his old self, giving up three runs and eight hits in seven innings, striking out seven and walking just one.
"It felt really good to have a game like that," Jimenez said. "The last five games that I had have been really bad and today I was able to locate the fastball."
|More on Giants at Rockies|
Jimenez said the outing gave him confidence that he's getting back to being his old dominant self.
Through seven innings it appeared as though the Giants were going to get their sixth win in eight tries against the Rockies and leave town with a 1 ½-game lead over their rivals.
"It's nice to walk out of here being in first place," Tulowitzki said. "They have been beating us up the whole year, so it's nice to kind of answer back, throw a few punches and prove to them that we're going to be in this thing for the long haul."
Gonzalez, whose three-run homer off Tim Lincecum propelled Colorado past the Giants 7-4 on Monday night, grounded a fastball to right field to snap a 3-3 tie in the eighth and make a winner of Matt Belisle (4-2), who worked one inning of relief.
It was the first time all season that the Rockies won a game in which they trailed after seven innings.
Jonathan Sanchez (3-3) allowed three hits and didn't walk a batter over the first seven innings but gave up back-to-back singles to Ryan Spilborghs and Chris Iannetta leading off the eighth, then threw away Alfredo Amezaga's sacrifice bunt, allowing Spilborghs to score from second base and pull Colorado to 3-2.
"It was an easy out at first," Sanchez said. "I should have made that play I think that's why we lost. Amezaga is pretty fast and I just wanted to make sure I got him out and I threw the ball away."
His blunder was reminiscent of the night before, when Lincecum's throwing error led to four unearned runs.
"That's the third time on this road trip where we've thrown the ball away and it's hurt us," said Giants manager Bruce Bochy, who promised his pitchers would be doing some spring training drills this week.
Aside from Sanchez's bad throw to first, Bochy couldn't complain about his lefty who had walked 14 batters in his previous three starts but had pinpoint control Tuesday.
Lopez replaced Sanchez and Dexter Fowler sent his ninth pitch over the center fielder's head for a ground-rule RBI double to tie it at 3.
One out later, Gonzalez pulled a fastball to right to score Amezaga and Fowler.
"He likes to go corner to corner, and after I saw the first-pitch cutter away, I was just expecting something close to me on the inside part. He tried to come in and I was ready for the pitch," said Gonzalez, who was admonished by his teammates to calm down after he took a big swing at the first pitch in the dirt.
Gonzalez stepped out, gathered himself and delivered another game-winner for the Rockies and backbreaker for the Giants.
"If the season ended today, I supposed we'd be panicked," Lopez said. "But, I mean, we've got three quarters left so I think we're OK."
Tulowitzki tied it at 1 when he led off the bottom of the second with his 11th homer after Miguel Tejada's RBI single in the top half, but the Giants grabbed the lead right back on Pat Burrell's two-run double in the third, when he sent Jimenez's 96 mph heater on a 3-and-0 count into the gap in left-center, driving in Mike Fontenot and Buster Posey, who had reached on two-out singles.
Jimenez worked out of two more jams, including one in the seventh when Sanchez led off with a double and was stranded at third.
Jimenez cracked the cuticle on his right thumb on the eve of the opener last month, and the injury zapped the zip from his fastball and stole the spin from his breaking pitches. After his first career stint on the disabled list, he had been unable to find any consistency, command or confidence.
The Rockies pored over film from last year's 15-1 start and compared them to this year. They discovered he was rocking back too far in his delivery and so they tweaked things during side sessions over the weekend.
It worked wonders.
"I didn't even have to think when I got to the mound," Jimenez said. "I didn't have to worry about my mechanics because I was repeating it every time. It felt really good."
- Giants IF Freddy Sanchez took the day off with swelling in his left knee that's bothered him for a couple of days.
- The Giants hadn't lost a series since April 29-May 2 against Washington.
- Tulowitzki's 11 homers lead all major league shortstops.