PITTSBURGH -- Marlon Byrd is experienced at making first impressions. The 37-year-old outfielder is with his 10th team.

Byrd couldn't have made a much better debut Friday night, as he collected three hits, including a home run, in his first appearance for the Giants as San Francisco beat the Pittsburgh Pirates 6-4 on Friday night.

Giants left-hander Madison Bumgarner earned his 15th win and hit his fifth homer of the season.

San Francisco acquired Byrd from the Cincinnati Reds on Thursday in exchange for a minor league pitcher.

"We needed a shot in the arm, and he gave us a lot more than that," Giants manager Bruce Bochy said.

Byrd, who played right field, hit a two-run home run during a three-run first inning. He also doubled while going 3-for-5 after going just 5-for-33 (.152) in his last 10 games with the Reds.

"I'm really excited about being here," Byrd said. "It's a great situation. These guys know how to win.

"It was one of those nights where I put some perfect swings on some good pitches, took some good swing paths."

Bumgarner (15-6) allowed three runs and six hits in 6 1/3 innings with six strikeouts and one walk. He tied Chicago Cubs right-hander Jake Arrieta for the National League lead in wins.

The left-hander also hit a two-run homer in the second inning while winning his fourth consecutive start. Bumgarner has the most home runs in a season by a major league pitcher since Carlos Zambrano hit six for the Cubs in 2006.

"I've watched him hit home runs on ESPN and MLB (Network), but it's fun to see it in person," Byrd said. "He's like having a ninth hitter in the lineup."

The Giants' six runs were as many as they scored in their previous four games combined, a span in which they went 1-3.

Left fielder Nori Aoki also had three of the Giants' 14 hits. First baseman Brandon Belt and center fielder Gregor Blanco added two hits each.

Closer Santiago Casilla pitched a scoreless ninth inning for his 30th save.

That came after the Pirates cut the lead to 6-4 on pinch hitter Neil Walker's sacrifice fly in the seventh and third baseman Aramis Ramirez's single in the eighth. Ramirez's hit scored center fielder Andrew McCutchen, who had doubled.

The Pirates, though, failed to take advantage of Bumgarner before he settled down to 14 batters in a row from the second through the sixth innings.

"We had a couple push situations on him early," Pittsburgh manager Clint Hurdle said. "We were able to chip him for a run in the first two innings and (had) some opportunities to add on. We weren't able to push through on those."

San Francisco (66-56) climbed within 1 1/2 games of the Los Angeles Dodgers in the National League West and remained 4 1/2 games behind the Cubs for the second NL wild card.

Pittsburgh (72-48) lost for the just the second time in nine games overall and the fifth time in its last 23 home game as its lead in the NL wild-card race over the Cubs was sliced to three games.

Pirates left-hander Jeff Locke (6-8) was tagged for six runs and 11 hits in five innings. He has failed to pitch at least six innings in any of his last six starts, going 1-2 with a 6.39 ERA in that span.

"I just never really got in any kind of groove," Locke said.

McCutchen, first baseman Michael Morse and right fielder Sean Rodriguez had two hits apiece for the Pirates. Left fielder Starling Marte extended his hitting streak to six games.

The Giants broke to a 5-2 lead after two innings by scoring three runs in the first and two in the second.

Catcher Buster Posey opened the scoring with a sacrifice fly, and Byrd followed with his homer run to make it 3-0.

In the second, Blanco doubled and scored on Bumgarner's home run, increasing the Giants' lead to 5-1.

The Pirates scored single runs in each of the first two innings. Rookie shortstop Jung Ho Kang hit an RBI single in the first, and Marte brought home a run in the second on a fielder's choice grounder.

Belt's RBI double in the fourth pushed the Giants' lead to 6-2.

NOTES: San Francisco will activate RHP Mike Leake (0-1, 2.84 ERA) from the 15-day disabled list Saturday afternoon and start him against Pittsburgh RHP Gerrit Cole (14-7, 2.61 ERA) in the third game of the four-game series. Leake went on the disabled list Aug. 3 with a strained left hamstring after making only one start for the Giants following his acquisition from Cincinnati. ... OF Marlon Byrd reported to the Giants a day after being acquired from the Reds and started in right field, batting fifth. RHP Chris Heston was optioned to Triple-A Sacramento. The Giants want to rest the rookie, who has pitched 145 2/3 innings while going 11-7 with a 3.34 ERA in 24 starts, including a no-hitter against the Mets on June 9 at New York. ... Pittsburgh INF/OF Josh Harrison was activated from the 15-day DL and started at second base after being out since July 6 with a torn ligament in his left thumb that required surgery. RHP Josh Wall was designated for assignment.