SAN DIEGO -- Being swept was in the back of the San Francisco Giants' minds going into the finale of a three-game series against the San Diego Padres on Sunday at Petco Park.

"This was a big game for us," San Francisco manager Bruce Bochy admitted after the Giants held off the resurgent Padres 5-3 behind Johnny Cueto's pitching and back-to-back, third-inning homers from Hunter Pence and Buster Posey. The Giants snapped a four-game losing streak.

"The last thing we wanted to do was get swept here and go 1-6 on this road trip going into the home opener Monday."

But after putting the tying runs on base in the ninth, closer Mark Melancon got a double-play grounder from Padres first baseman Wil Myers on the game's final pitch.

"Today was all about winning at all costs," said Melancon, who picked up his first save as a Giant after blowing his first opportunity in the season opener. "You're going to go through s stretch like this at some point of the season. You just don't want to do it at the beginning of the year."

"Thank God, everything worked out and we didn't get swept," said Cueto, who has both of the Giants' wins this season.

Cueto (2-0) continued his domination of the Padres, holding them scoreless through 5 1/3 innings while San Francisco was building a 5-0 lead against San Diego left-handed starter Clayton Richard.

The Pence and Posey homers capped a five-run, two-inning Giants' assault of Richard, who had opened the season with 9 1/3 straight scoreless innings. Posey played a role in both rallies.

The catcher walked to open the second inning, moved to third on Brandon Crawford's single and scored when Chris Marrero became the first Giants' left fielder to get a hit this season. Crawford also scored when the throw from Padres right-fielder Hunter Renfroe ricocheted off first baseman Myers into the Padres dugout.

Brandon Belt walked with one out in the third ahead of Pence's 351-foot homer to left. Posey followed with a 362-foot drive to right. It was the first homer of the season for both and the first back-to-back homers for the Giants this season.

"The Pence homer, sometimes you have to tip your cap to the hitter," said Richard, who yielded five runs (four earned) in six innings. "He went down and hit what I thought was a pretty good pitch. Posey was a little more disappointing. I fell behind 2-and-0 in the count, leaving him to pick one pitch to hit. Overall, I executed a majority of my pitches."

So did Cueto, who last season was 3-1 against the Padres with a 1.41 ERA, logging three complete games in four starts. He had retired 11 straight Padres for 5 1/3 innings before walking Travis Jankowski with one out in the sixth.

Myers, who had been 1-for-16 lifetime against Cueto coming into the game, followed with his second homer of the season, a 354-foot drive to left, to cut the Giants' lead to 5-2. The Padres then loaded the bases, but Cueto got out of the jam by retiring Erick Aybar on a pop out to third.

Cueto worked seven innings and allowed two runs on five hits and three walks. He struck out seven.

"Cueto was really good early on," said Padres manager Andy Green. "He disrupted our timing, but as the game went on, we got better and better at-bats."

Padres cleanup hitter Yangervis Solarte greeted San Francisco right-handed reliever Derek Law with a 346-homer to open the eighth to make it 5-3.

With one out in the bottom of the ninth, Melancon gave up a single to Manuel Margot, then walked Jankowski before getting Myers to ground into the double play.

"It got a little scary there, but he made a pitch when he had to," Bochy said of Melancon.

NOTES: The Padres placed RHP Trevor Cahill on the 10-day disabled list due to a back injury, and they promoted RHP Zach Lee from Triple-A El Paso. Cahill was scheduled to start Monday against the Rockies in Colorado. ... RHP Hunter Strickland will rejoin the Giants for Monday's home opener after being away from the team on paternity leave.