CINCINNATI -- Optimism was abundant in the San Francisco Giants' clubhouse on Friday night. Nothing like a 10-run outburst and the impending return of a key player to rekindle hopes for the defending World Series champions.

Brandon Belt and Buster Posey homered and Madison Bumgarner pitched seven solid innings, lifting San Francisco to a 10-2 victory over the Cincinnati Reds at Great American Ball Park.

The 13-hit attack came hours after the news that Hunter Pence was rejoining the team on Saturday.

"We get our big guy back," Belt said. "That's huge for us. Definitely builds some confidence for us on the offensive side. It's a chance to build some momentum."

About the only drama in came in the sixth inning when one of the Power Stacks beyond center field at Great American Ball Park, made to resemble steamboat smokestacks and used as a home-run feature, caught fire, sending thick smoke throughout the ballpark.

Two sections of stands were evacuated while firemen extinguished the flames. The game wasn't interrupted. A propane valve malfunction was cited for the blaze.

"I felt sorry for the guy who had to go up there on the ladder," Giants manager Bruce Bochy said. "I know that's what they have to do, those firefighters. Didn't want to see him go to the moon right there."

Center fielder Billy Hamilton and shortstop Zack Cozart homered for Cincinnati (18-18), which had a three-game winning streak snapped.

Shortly after the fire was put out, the Giants, already leading by four runs, erupted for three more in the seventh off rookie right hander Michael Lorenzen.

Run-scoring doubles from Belt and right fielder Jason Maxwell and an RBI single by shortstop Brandon Crawford pushed San Francisco's lead to 9-2.

Belt went 3-for-5 with a double, homer and four RBIs to pace a 13-hit attack by San Francisco, which moved back to .500 (18-18) for the seventh time this season.

After allowing Cozart's home run in the first inning, Bumgarner (4-2) mostly cruised, giving up two runs and eight hits. He allowed two homers but didn't walk a batter.

"Our offense hit the ball real well," Bumgarner said. "Gave me the freedom to attack guys a little more. You've got to still make pitches."

Conversely, Reds starter Jason Marquis (3-2) allowed six earned runs and seven hits, including two homers, in a season-low three innings.

"I'm just not very good right now," Marquis said. "I can't throw pitches consistently like I want to. I'd better figure something out quick. This is not fun."

San Francisco didn't waste any time getting to Marquis.

Left fielder Gregor Blanco walked leading off the game and second baseman Joe Panik followed with a single.

With two outs and on the first pitch from Marquis, Belt hit a towering home run into the visitor's bullpen in right field, putting the Giants ahead 3-0.

"That one would've been in the water in San Francisco," Bochy said.

It was Belt's first home run since Sept. 25.

"I forgot what it felt like," he said.

Cincinnati got a run back in the bottom of the first when Cozart hit his sixth homer of the season.

But Posey's two-run blast in the third, his sixth homer of the season, made the score 5-1. Third baseman Casey McGehee added an RBI single later in the inning.

"It was going to be a challenge to get back in the ballgame against Bumgarner," Reds manager Bryan Price said. "He had great stuff as usual."

That was it for Marquis, who has allowed five homers in his last 8 2/3 innings.

Bumgarner elevated an 0-2 pitch to Hamilton, who sent it into the left field seats in the fifth. Hamilton's third homer of the year made the score 6-2.

By then, only the fire kept the crowd of 39,867 amused as the Giants enjoyed their highest scoring output at Great American Ball Park since 2007.

"Good bounce back for us after a couple of tough losses," Bochy said. "We had a rough start. We wanted to hold fort until we got Hunter, one of our core guys, back. I'm proud of the guys."

NOTES: Giants RF Hunter Pence, on the disabled list since fracturing his left forearm in the third spring training game, will rejoin the club in Cincinnati on Saturday and likely will be activated. Pence went 5-for-17 with two homers and five RBIs during five rehab appearances at Triple-A Sacramento. ... Reds 2B Brandon Phillips returned to the lineup on Friday after missing two games with turf toe. ... Giants RHP Matt Cain, on the DL with a sore right forearm, threw 30 pitches in a bullpen session on Thursday. He is expected to throw again on Tuesday and mix in breaking balls. ... Cincinnati's bullpen allowed four runs, six hits and two walks on Friday. Reds relievers came in ranked last in the National League with a 5.19 ERA.