SAN FRANCISCO -- Matt Cain contributed to a win in more ways than one Tuesday.

The San Francisco right-hander turned in a decent start and also belted a three-run homer during the Giants' 9-7 win over the Cincinnati Reds at AT&T Park.

Cain's blast capped San Francisco's four-run second inning, and he went 5 1/3 innings to win for the first time since May 21.

"I thought Matty threw the ball pretty good," Giants manager Bruce Bochy said. "(The) bats picked us up tonight."

Five relievers followed Cain (2-6), with closer Santiago Casilla surrendering a ninth-inning run before posting his 22nd save. Casilla ended the game by striking out Reds right fielder Jay Bruce, who represented the tying run. Bruce homered one inning earlier, the fourth game in a row he went deep.

"We don't do anything easy," Bochy said. "(We) faced some pretty good batters there at the end, but Casilla found a way to get that last out. Good job by him."

The Giants, who led 5-0 after three innings, held on for only their second win in 10 games following the All-Star break.

Reds manager Bryan Price said, "We gave Casilla a good ninth inning to get Jay up there with a chance to tie the ballgame. It was a good feeling to be able to come back and rally, it gave the guys a good sign."

Bochy said, "To get a win, no question, it's a good thing right now. We've been in a tough stretch."

The Reds drew within 6-4 following a two-run home run in the sixth inning by ex-Giant Adam Duvall -- the left fielder's first of two on the evening -- with the blast chasing Cain. It was a nine-pitch battle that included three consecutive two-strike foul balls by Duvall before he got a pitch to drive.

"I wasn't in a slump by any means, but I wasn't stringing them together as I would like to," said Duvall, who collected his 24th and 25th homers of the year. "But now I feel like I'm stringing some good at-bats."

The Giants restored their five-run margin by scoring three times in the seventh.

Cain allowed four runs on six hits and a walk with four strikeouts.

"I just did a better job keeping the ball out of the middle of the plate," Cain said. "I did a better job of eliminating mistakes."

Giants shortstop Brandon Crawford (3-for-5) collected his first two post-All-Star break RBIs with a triple to right-center after Mac Williamson and Buster Posey started the frame with singles. Crawford scored on a pinch single by Conor Gillaspie two batters later.

Cincinnati greeted Sergio Romo, the Giants' fourth reliever, with back-to-back home runs to start the eighth. Bruce launched his 24th of the season into the right field arcade on Romo's first pitch. Duvall followed by sending a homer into the left field bleachers on a 2-1 pitch.

Romo surrendered a single to Brandon Phillips, then settled down by inducing a double-play grounder from Eugenio Suarez and a groundout from Ramon Cabrera.

The Giants jumped on Reds starter Cody Reed (0-5) for four runs in the second inning. With better defense, the winless left-hander might have escaped the inning unscathed.

Crawford reached when his line drive deflected off the glove of Reds shortstop Zack Cozart, who was not given an error on the play. Brandon Belt followed with a drive to deep left-center that Duvall dropped after a long run for a two-base error.

Following a broken-bat ground out by Grant Green, Ramiro Pena hit a ball into the hole that Cozart kept on the infield with a dive. Crawford scored, and Belt was ruled safe at third following a review overturned an initial out call on Cozart's throw to third baseman Suarez.

One pitch after Cain fouled off a bunt attempt, the pitcher drove a fastball deep into the left field bleachers for a three-run home run. Cain's seventh career round-tripper was his first since July 21, 2012, in Philadelphia.

"You're hoping he can get one run in," Bochy said of Cain. "He got a pitch he could handle. He has big power when he gets a hold of it."

Cain said, "It's just nice to go out there and contribute. That situation, you're just looking to help out the guys when you're at bat. It turned out pretty good."

The hosts tacked on their fifth run an inning later.

Williamson singled, advanced to third on consecutive singles by Crawford and Belt, and scored on Green's groundout to second that was initially ruled an inning-ending double play until San Francisco's successful challenge that Phillips missed his tag of Belt before relaying a throw to first.

Cincinnati got a run back when Joey Votto launched his 18th home run over the left-center-field fence on an 0-1 pitch to lead off the fourth inning.

The Reds scored again in the fifth when Billy Hamilton stroked a two-out single to right to chase home Suarez, who led off the inning with a single.

San Francisco answered in the bottom half when Green lined a one-out sacrifice to right to plate Posey, who singled and stole third base after advancing to second on a wild pitch.

Reed was charged with six runs (five earned) on nine hits and two walks in five innings. He struck out three.

NOTES: The Giants have allowed 23 home runs in their 10 games since the All-Star break -- 18 of which were surrendered by starting pitchers. ... The Reds brought the majors' best winning percentage against the Giants (.596, 34-24) since 2008 into Tuesday's contest. ... San Francisco 3B Matt Duffy (Achilles strain) and RHP Cory Gearrin (shoulder strain) made on-field progress at AT&T Park on Tuesday toward possible rehab assignments by the weekend. ... Four Reds starters extended hitting streaks in Tuesday's game: 2B Brandon Phillips (14 games), 1B Joey Votto (11), CF Billy Hamilton (nine) and RF Jay Bruce (eight). ... Giants manager Bruce Bochy opted to give Brandon Belt another start on Tuesday after suggested it would be a day off for the first baseman who struggled on the recently completed road trip. Belt went 3-for-4 with his 11th home run Monday during a 7-5 loss in the series opener against Cincinnati. Belt went 1-for-2 with three walks Tuesday.