PHOENIX -- Someone, it seemed, always picked up the slack and provided what was needed for the San Francisco Giants during their World Series run last year. The same thing is happening now.

Barry Zito went down in the second inning with a sprained right foot Saturday night but Guillermo Mota came on for 4 1/3 innings of solid relief, his longest stint in 672 major league appearances over 13 seasons, and the Giants won their fourth straight, 5-3 over the Arizona Diamondbacks.

"It's tough for Barry. I don't know what happened or the severity of it, but hats off to Guillermo Mota," teammate Mark DeRosa said. "Player of the game, no doubt."

Zito was on crutches, the middle of his right foot noticeably swollen, as he contemplated the possibility that he might miss a start due to injury, something that's never happened to him in his major league career. He came back from a car accident on the eve of opening day to make his regularly scheduled first start.

"Yeah," he said when asked if the streak crossed his mind. "When I feel my foot, it's pretty painful. I couldn't throw my [practice] pitch too well, but there are incredible things that can happen.

"I was able to recover from that accident and that was huge, so we'll see. We'll see what the MRI says tomorrow and just go out and take it day by day."

Freddy Sanchez doubled in the tying run in the sixth inning, then put San Francisco up for good with a two-run single in the seventh.

"The depth of this team was something that was a positive for us last year and I think this year it's the same," DeRosa said.

Mota (1-0) allowed one run and three hits, striking out four with no walks.

"He knew coming into spring training that would be a role for him if he was on this club," manager Bruce Bochy said. "He worked hard, stretching his workload out, multiple innings. Talking to him at the end of spring training he said that he knew that this would be his role, and he's a pro. To his credit, he got himself ready to handle a situation like this."

The Diamondbacks tied a franchise record by converting five double plays to erase a big share of San Francisco's 13 hits.

Buster Posey hit a two-run homer in the first inning off Joe Saunders (0-3), who gave up five runs on 12 hits in 6 2/3 innings.

Brian Wilson pitched a perfect ninth to give him a save in each of the Giants' four straight wins. The reigning World Series champions have won seven of nine after opening the season 1-4.

Sanchez's RBI double tied it at 3. Singles by Pat Burrell and Mark DeRosa and a walk to Aaron Rowand loaded the bases with two outs in the seventh, ending Saunders' day.

Sam Demel relieved the Arizona starter and Sanchez's soft single between third and shortstop brought in two runs to put the Giants back ahead, 5-3. The Diamondbacks lost their third straight and fell to 3-5 on a nine-game homestand that ends with the series finale against San Francisco on Sunday.

"We didn't match their bullpen," Arizona manager Kirk Gibson said. "They got 7 1/3 innings from their 'pen. The way I had my lineup set up with all the righties in there and Zito goes out after 1 2-3. Their bullpen responded as good as you can ask, giving up one run. When it rains it pours. Right now we have to fight through it."

Arizona scored two off Zito in the second on doubles by Chris Young and Miguel Montero, sandwiched around a four-pitch walk to Xavier Nady. That brought up Saunders, who bunted toward the mound. Zito appeared to catch his right spike in the turf as he lunged to make the catch.

After he was unable to continue, Mota came on to get Willie Bloomquist to bounce out to end the inning.

Arizona took a 3-2 lead on Melvin Mora's RBI double, with the 39-year-old Diamondback tagged out by several feet trying for third on the play.

Posey's second home run of the season came with two outs on a 1-2 pitch, the ball making it to the seats in left-center, to the left of a 413-foot sign.

Game notes
Bloomquist went 0 for 4, ending a 10-game hitting streak that was tied for a franchise best to start a season. ... Montero has reached base in all 12 games, 10 of them on hits. ... The Giants have homered in the first inning in both games to start the Arizona series. Pablo Sandoval had a three-run shot in the 5-2 victory Friday night. ... Bochy turned 56 on Saturday. ... The five Diamondbacks double plays came in the first six innings.