OAKLAND, Calif. -- The San Francisco Giants stayed alive in the National League West title race for at least another day.

Rookie right-hander Chris Heston snapped his five-game losing streak as Giants built a quick five-run lead then held on for a 5-4 victory against the Oakland A's on Sunday afternoon at the O.co Coliseum.

The Giants pulled to within six games of the first-place Los Angeles Dodgers, who lost 12-5 to Colorado, with seven to play. The Giants and Dodgers open a four-game series Monday night at AT&T Park.

"Keep fighting," Giants manager Bruce Bochy said. "As I said so many times, you never know. We wish we were in a little better position. We lost some tough ones on this trip here, those two in San Diego and the first one here."

Heston (12-10) gave up four runs on six hits, lasting five-plus innings. He struck out three, walked two and threw 78 pitches. Heston won for the first time since Aug. 1 at Texas.

"It feels great to get back in the win column," Heston said. "It's been a while since I personally got a win, but the team win, we need a lot of wins right now obviously, so it's good we walked away with the W."

The Dodgers' magic number is two, so they can clinch the West with one victory against the Giants.

Five Giants relievers combined to blank Oakland over the final four innings: George Kontos, Cory Gearrin, Javier Lopez and Santiago Casilla, who pitched a scoreless ninth with one walk and three strikeouts for his 37th save.

"The bullpen really stepped up," Bochy said.

The A's lost two of three in the series to their Bay Area rivals and finished the year 1-5 against San Francisco and 34-47 overall at home.

"Disappointing," A's manager Bob Melvin said. "Our fans tried to pick us up and carry us through. It would have been nice to win the series here, definitely, to end the season for them. Because they came out really enthusiastic for us."

Giants left fielder Jarrett Parker, who hit a franchise rookie record three homers Saturday, went 2-for-3 with a walk and scored a run. Rookie designated hitter Mac Williamson had two hits in three at-bats, drove in a run and scored once. Catcher Trevor, another rookie, drove in two runs, and rookie second baseman Kelby Tomlinson had a pair of hits and an RBI.

"Mac's been coming up playing real well," Parker said. "Trevor's done a great job behind the plate and swinging it too. Its' awesome to see the guys come up and contribute for sure."

A's left-hander Sean Nolin lasted only 2 2/3 innings, his shortest outing in five starts since being recalled from Triple-A Nashville on Sept. 4. He gave up five runs, only three of them earned, on seven hits, struck out one and walked on.

"It was not a very good outing," Nolin said. "I feel like I made some good pitches definitely. They put the barrel on the ball and ended up getting some hits on them. And then the sacrifice flies, the pitches got away and they were kind of just left there to hit."

The Giants grabbed a 3-0 lead in the top of the second inning. Shortstop Brandon Crawford led off with an infield single, Parker lined a single to center, and Williamson grounded a single to right, loading the bases with no outs. Brown and center fielder Angel Pagan hit back-to-back sacrifice flies, making it 2-0, then Tomlinson hit an RBI single to right.

The Giants added two runs in the third. First baseman Buster Posey led off with a single to center, moved to second on right fielder Marlon Byrd's ground out and went to third when second baseman Brett Lawrie made a throwing error on Crawford's ground ball.

Parker walked, loading the bases and ending Nolin's day. Williamson brought Posey home with a sacrifice fly, and Brown hit a soft single to center, driving in Crawford.

The A's cut San Francisco's lead to 5-2 in fifth, as center fielder Billy Burns hit a fly ball to shallow center that bounced off of Crawford's glove for a two-run double.

Oakland scored two more runs in the sixth. Third baseman Max Muncy hit an opposite-field RBI triple off the wall in left. Parker slammed hard into the wall while trying to catch Muncy's drive but stayed in the game.

"I got it pretty good," Parker said. "It rattled me a little bit. I got my leg caught under me a little bit, but I ended up being fine."

Muncy entered the game in the top of the fifth, replacing Danny Valencia, who was hit by a pitch on his left elbow in the fourth inning. X-rays on Valencia's elbow were negative, but he's day-to-day, Melvin said.

NOTES: A's manager Bob Melvin called RHP Sonny Gray's chances of making his next scheduled start Tuesday a "long shot" because of a sore left hip. Melvin will make that decision Monday. ... Giants manager Bruce Bochy said he expects RHP Tim Hudson to make his scheduled start Thursday against the Dodgers at AT&T Park, but he also said there's a chance Hudson could have his start pushed back. ... A's LHP Barry Zito, Giants RHP Tim Hudson and former A's LHP Mark Mulder, who comprised Oakland's "Big Three," threw out the ceremonial first pitches and were honored during a pregame ceremony. ... A's RHP Edward Mujica (strained right hamstring) pitched for the first time since Sept. 13 and threw a scoreless inning in relief.