One night after Travis Ishikawa won the game with a three-run homer in the eighth inning, Bengie Molina hobbled off the bench Wednesday and did the same, although his was more dramatic because his two-out shot against Arizona closer Chad Qualls turned a two-run deficit into a 4-3 victory.

Big Money's simple message after his third career pinch homer moved the Giants three games behind the Rockies for the National League wild card: Do not let up.

"I hope it's a big lift," Molina said. "I hope everybody gets pumped up for tomorrow and plays the right way and keeps going."

The Giants really are riding a bicycle at full speed. With 35 games remaining, they cannot stop pedaling or they will crash, dooming their underdog playoff hopes.

They have not enjoyed many big runs this season. Their longest win streak is five games. They won 10 of 15 heading into the All-Star break and 10 of 14 in late July and early August. But they need more. They need to finish August with a great homestand and start rolling.

Pessimists have a reason for concern. The Giants do not seem to have the consistency at the plate to sustain a long run.

On Wednesday, their offense was dead in the water most of the night with Molina (quad strain) and Pablo Sandoval (calf strain, flu) unable to start. Those two have driven in more than one-quarter of the team's 514 runs.

The Giants did not score against junkballer Doug Davis until Juan Uribe homered, for the second consecutive night, in the seventh inning. They had only three hits until Randy Winn blooped a single to right in the eighth after Edgar Renteria's second walk of the game started the winning rally with two outs.

"To win a game like this, it's huge for a ballclub, especially when there wasn't a lot happening there until Bengie bailed us out," manager Bruce Bochy said.

When Winn singled, Arizona manager A.J. Hinch replaced the left-hander Davis with Qualls. Ryan Garko was due to hit. Bochy bypassed left-handed hitters Ishikawa and Nate Schierholtz and sent Molina to hit because he was 3-for-5 against Qualls.

The closer got ahead of Molina 0-2 and tried to get a slider past him. Instead, Molina sent it soaring high into a foggy night and barely over the left-field wall for his 16th homer of the season.

"I'm a guy who likes to play games," said Molina, who appreciated the crowd's chants of "Ben-gie, Ben-gie" that prompted a curtain call. "I don't like being on the bench. I like to be part of the game. To do that, it's an amazing feeling."

Pitching was a big part of the story, too. On a night that Brian Wilson and Jeremy Affeldt were unavailable because of too much use, Jonathan Sanchez gave Bochy seven innings, holding Arizona to Ryan Roberts' game-opening homer and a pair of RBI singles in the sixth.

Justin Miller got the win with a scoreless eighth in his first appearance since a dreadful performance in the 14th inning of Monday's loss in Colorado, the lowlight his bases-loaded walk to pitcher Adam Eaton.

Giants fans booed Miller as he trotted to the mound. He heard them, too.

"I understand where they're coming from," he said. "What happened in the past is the past. I'm just looking forward to another month of exciting baseball."

Brandon Medders earned his first career save. Sergio Romo was supposed to close but did not have enough time to warm up, given the speed with which Molina rewrote this story.

E-mail Henry Schulman at hschulman@sfchronicle.com.

This article appeared on page B - 1 of the San Francisco Chronicle