Padres 2, Giants 0: Alexi Amarista homered and Eric Stults tossed seven strong innings as San Diego blanked visiting San Francisco in the opener of a three-game series.

Chase Headley went 4-for-4 - including an RBI single during a two-run third inning - and Amarista added a double and reached base three times to help the Padres extend their winning streak to a season-high five games. San Francisco, which was shut out for the third time in its last five contests, lost its third in a row and has dropped 18 of its past 23 games.

Stults (3-11) earned his first win since May 10 while yielding four hits and two walks, and Huston Street retired the Giants in order in the ninth for his 23rd save. Stults, who lost all six of his starts last month, matched his longest start of the season and did not allow a run for the first time in 18 starts.

The Padres scored the only run they would need when Amarista belted his second homer of the season off Matt Cain (1-7) and Headley followed Seth Smith’s double with an RBI single to left-center field. Cain allowed two runs on seven hits in 6 1/3 innings and remained winless in seven straight starts since May 15.

The Giants’ best scoring threat came in the second as Juan Perez drew a two-out walk to load the bases before Stults struck out Cain to end the inning. Stults’ outing marked another strong performance from the Padres’ starting rotation, which has posted a 1.92 ERA over the last 15 games.

GAME NOTEBOOK: Giants 1B Brandon Belt was activated from the disabled list after missing eight weeks with a broken left thumb and went 0-for-4 while batting second. … Brooks Conrad made his Padres debut at second base and went hitless in three at-bats. … Headley’s four-hit game was the 12th of his career and first since Sept. 2, 2012.