SAN FRANCISCO -- It had been 60 days since Yadier Molina's last error and 62 since Buster Posey's last home run, but they both happened again Friday night.

Together, they helped produce all the San Francisco Giants' scoring in an 8-2 victory over the St. Louis Cardinals that resulted in a second consecutive win in the key four-game series.

"That's what you want to do -- take advantage of mistakes," Brandon Belt said after the Giants (79-68) used six unearned runs to open a three-game gap over the Cardinals (76-71) in the National League wild-card race.

Posey and Belt had two-RBI hits in a six-run third inning that was prolonged by Molina's throwing error.

Because of it, the Giants also were able to keep pace with the Los Angeles Dodgers atop the NL West. The Dodgers (83-64) retained a four-game lead with a 3-2 victory over the Arizona Diamondbacks.

"Confidence grows with success," Giants manager Bruce Bochy said of his club's second straight win after a stunning three-game sweep at the hands of the San Diego Padres to begin the week. "Get big hits. That's what good ballclubs do."

The loss dropped the Cardinals two games behind the New York Mets (78-69), who hold the second wild-card spot in the NL.

"We just have to play better, that's all there is to it," Cardinals manager Mike Matheny said. "The standings are the standings, and we know what they are. You can't run from them. The standings say we're right there, so just keep playing the game."

A questionable decision by the normally dependable Molina opened the floodgates for the Giants in the six-run third.

With one on and one out in a scoreless game, Molina fielded Giants pitcher Matt Moore's bunt in front of home plate and had an easy second out at first base. But he chose to rush a throw to second and threw high for an error, allowing Denard Span to slide in safely.

"That was the right play," Matheny insisted. "Ball out of in front of him. He makes that play 99 times out of 100."

The error was Molina's second of the season and first since July 18.

After Angel Pagan walked to load the bases, Joe Panik hit a fly ball to right field that would have ended the inning had the Cardinals gotten an out on the bunt. Instead, it went for a sacrifice fly, scoring the game's first run.

In fact, all three baserunners advanced on Panik's fly, setting up a two-run single by Posey on a blooper to right to make it 3-0.

The Giants weren't done. Hunter Pence singled, Belt laced a two-run double and Brandon Crawford smacked an RBI single, completing the six-run uprising, with all of the runs unearned.

"When you think about it, that's what you want to do in the playoffs," Belt said. "Don't make mistakes, and take advantage when the other team makes one."

Cardinals starter Luke Weaver (1-3) was pulled after Crawford's hit. The rookie allowed six runs (none earned) and five hits in 2 2/3 innings. He walked two and struck out four.

Belt was originally called out at the plate on Crawford's double, but the Giants challenged and the call was reversed.

It was the second overturn of the inning, with one costing the Cardinals a run in the top of the third.

It appeared St. Louis had scored the game's first run on a two-out infield single by Aledmys Diaz. But the Giants challenged the safe call at first, and got a run-saving reversal from New York.

The Cardinals got on the board in the fourth when Molina singled in Stephen Piscotty, who had walked.

But Posey countered immediately with his first home run in two months to make it 8-1.

"It was great to see him start smiling and laughing when he touched home plate," Belt said. "He's usually not like that."

Moore (11-11), staked to a big early lead, won for the fourth time in his last five starts. He allowed two runs and seven hits in five innings, walking three and striking out four.

Five Giants relievers combined to no-hit the Cardinals the rest of the way.

Posey, who had four hits in Thursday's 6-2 victory in the series opener, drove in four runs with three hits.

Belt had two hits for the Giants, who saw an 11-game errorless streak end when Moore made an errant pickoff throw to first base in the third inning.

Molina drove in two runs and Matt Carpenter had two hits for the Cardinals, who began a 10-game trip with a pair of losses.

Former Cardinals closer Trevor Rosenthal provided a positive for the club with a successful return from a nearly two-month stint on the disabled list with shoulder injury. He threw a 1-2-3 seventh inning, striking out two.

Both teams finished with seven hits.

NOTES: The Giants have won two in a row at home for the first time since Aug. 18-19 against the New York Mets. ... Ten of the Giants' 14 runs in the series have come with two outs. ... Cardinals manager Mike Matheny announced that OF Matt Holliday will take live batting practice before Saturday's game to test his fractured right thumb. Holliday has a pin in the thumb and hasn't played since Aug. 11. ... The Giants reinstated OF Gregor Blanco (sore right shoulder) from the disabled list. Blanco had missed the previous 22 games. ... New Golden State Warriors player Kevin Durant threw out the game's ceremonial first pitch.