SAN FRANCISCO -- San Francisco Giants closer Santiago Casilla didn't just record his 100th career save Monday night.

As manager Bruce Bochy proclaimed afterward, he "earned" it.

Casilla got the Giants out of an eighth-inning jam, then shut the door on the San Diego Padres in the ninth, a four-out save that reached a milestone and provided his team a 5-4 win in the opener of a three-game series.

"He earned his 100th save, I'll say that," Bochy boasted after the Giants continued a recent home mastery of the Padres. "I got him up to get a big out, and he got a big strikeout for us."

Angel Pagan drove in two runs with three hits and Madison Bumgarner posted his first win since Opening Day, helping the Giants beat the Padres for the 10th time in their last 12 meetings at AT&T Park.

Hunter Pence smacked his team-leading fourth home run of the season, a solo shot that gave the Giants the lead for good in the fourth inning, and Buster Posey added his third in the seventh inning to provide what turned out to be the difference-maker.

Casilla's heroics were required after the Padres, who were opening a six-game trip, got within 90 feet of tying the game in the eighth after run-scoring hits by Alexei Ramirez and pinch hitter Brett Wallace.

Left-hander Josh Osich came on to strike out Jemile Weeks with runners on first and third for the second out. Then after pinch runner Travis Jankowski stole second to put the potential go-ahead run in scoring position, Casilla fanned pinch hitter Jose Pirela to avoid further damage.

"He knows what he's doing," Bumgarner praised of Casilla. "Pretty much every time he comes through for us."

Casilla stayed on to pitch a one-hit ninth, earning his fourth save of the season, the sixth of his career that required four or more outs.

Batting ninth, Pagan had a run-scoring single in the second inning and an RBI double in the fourth, both off Padres left-hander Drew Pomeranz (2-2), improving his season average with runners in scoring position to .600 (9-for-15).

The two RBIs gave him 11, three off Pence's team lead, despite his regular slot at the bottom of the order.

"It's working," Bochy noted. "He's in his comfort zone and the fans are behind him. I think he likes hitting there."

The Giants' 12-hit attack benefitted Bumgarner (2-2), who hadn't won since April 4 at Milwaukee.

The staff ace gave up single runs in the third and sixth inning before exiting two outs into the seventh, having given up six hits. He walked two and struck out nine, the fourth consecutive time he whiffed at least nine Padres.

Bumgarner snapped a three-game losing streak during which he went up against the Los Angeles Dodgers' Clayton Kershaw twice and Arizona Diamondbacks' Zack Greinke.

The Giants, who won for just the third time in eight games on their current 10-game homestand, haven't lost four straight Bumgarner starts since Aug. 7-Sept. 3, 2013.

Joe Panik had three hits, including a triple, and Posey two for the Giants, who out-hit the Padres 12-11 and improved to 9-0 when recording more hits than the opponent.

Matt Kemp doubled twice, singled and scored twice for San Diego, which began a six-game trip.

"Casilla has saved 100 games. He knows what he's doing out there," Padres manager Andy Green praised. "We had some pretty good swings against him. We had the winning run on second in the eighth and the winning run at the plate in the ninth. All you can ask is to give yourself a chance."

Pomeranz, who allowed a total of just four runs in his previous three starts, got tagged for four (three earned) in 4 1/3 innings by the Giants. He allowed seven hits and three walks while striking out six.

Pomeranz hurt himself with walks early on. He issued one to Brandon Belt in each of the first baseman's first two plate appearances -- both times with no one out -- and it cost him a run both times.

"I wasn't going after them like I had been the past few games," Pomeranz admitted. "I got into a lot of bad counts and that drove my pitch count up. I struggled. I know what I did wrong, and in two days I'll correct it and go from there."

NOTES: Giants LF Angel Pagan recorded all three of his hits with two outs. He's now 11-for-19 (.579) when batting with two outs this season. ... San Francisco LHP Madison Bumgarner became just the sixth pitcher to record nine or more strikeouts against the Padres in four or more consecutive games. ... San Diego LHP Drew Pomeranz raised his strikeout total to 31 in four starts. Only two pitchers -- RHP Jake Peavy (34) and RHP Stan Spencer (32) -- have begun their Padres career with more strikeouts in their first four starts.