SAN FRANCISCO (AP) -When manager Bruce Bochy came trotting to the mound to visit Matt Cain with NL saves leader Brian Wilson already warming up, it looked as if Cain's fine day might be done.

Instead, Cain got to finish the job - and that meant working out of trouble with the game on the line.

Cain pitched a four-hitter, Dave Roberts singled home a run in the eighth inning and the San Francisco Giants earned their first three-game home sweep of the season Thursday with a 1-0 win over the Washington Nationals .

''It's definitely very satisfying to get out with two guys on - to get out of a sticky situation,'' Cain said.

Cain (6-8), the hard-throwing right-hander who's had his share of hard luck the past two seasons, retired his first 11 batters and didn't issue a walk for the first time this year. After going 0-2 in his previous three starts, he struck out four in an efficient, 113-pitch performance to boost his strikeout total to 130.

Cain's only other shutout came May 21, 2006, at Oakland. This was the Giants' seventh shutout this year and the 13th time Washington has been blanked, a major league high.

With his fourth career complete game, Cain became the first San Francisco pitcher to throw a shutout since Noah Lowry on Aug. 21, 2006, against Arizona. The Giants' last complete game was by Matt Morris on June 11 last year against Toronto.

Washington's Cristian Guzman doubled with one out in the ninth to put runners on second and third, and that's when Bochy came out to talk to Cain. The pitcher had been fighting a cold earlier and Bochy just wanted to make sure he was fine to finish.

Ryan Zimmerman flied out to right, and Randy Winn made a perfect throw home to catcher Bengie Molina to hold the runner at third. Cain then got Austin Kearns to fly out to right to end it.

''He gave me a pitch to do the job and I just didn't hit it deep enough,'' Zimmerman said. ''I wasn't surprised that they didn't walk me.''

The Giants did consider it, though.

''I told myself I almost wanted him to beat me and I would challenge him and see what he could do,'' Cain said.

San Francisco took all seven games from the Nationals this year after sweeping a four-game set in Washington from June 6-9 - just the third time since 1900 the franchise has swept a season series of more than three games. San Francisco went 9-0 against Florida in 1998 and 6-0 versus the New York Mets in 2002.

Roberts started in left and batted leadoff, his first time in the lineup since going on the disabled list in late April following left knee surgery. The 36-year-old Roberts made a pretty, leaping catch that brought him to the ground, stealing a hit from Willie Harris in the sixth.

The Giants suddenly have some momentum heading into a weekend series at home against the first-place Diamondbacks.

''Basically for 3 1/2 months of the season I've been a fan,'' Roberts said. ''To come back, I lost a lot of sleep last night looking forward to today. I was tossing and turning waiting for my alarm to go off and get to the ballpark. ... To win three games going into the Arizona series is big for us. It was fun.''

Zimmerman doubled with two outs in the fourth for Washington's first hit. Since returning Tuesday from a 48-game absence with a shoulder tear, Zimmerman is batting .417 (5-for-12) and owns a 12-game hitting streak dating to before his stint on the disabled list. Starting pitcher Tim Redding was the next base runner against Cain after he singled in the sixth.

Redding (7-5) pitched his first career complete game and held tough right along with Cain until giving up Steve Holm 's leadoff single in the eighth. Eugenio Velez entered as a pinch runner and scored on Roberts' base hit up the middle. Had Holm not reached base, Bochy was prepared to pinch hit for Cain.

''We finally got the hit we needed,'' Bochy said. ''He shut us down offensively. Matt kept throwing zeros up there.''

Redding allowed seven hits in eight innings, struck out five and didn't walk a batter for the second time in three starts.

''Obviously, I feel bad for the young man,'' Nationals manager Manny Acta said. ''I know if he had more run support he would have a few more wins. It's a team game and he knows we appreciate what he's done.''

Bochy rested several regulars, including Molina, left fielder Fred Lewis and shortstop Omar Vizquel .

Guzman, who on Tuesday received a two-year contract extension worth $16 million, went 1-for-4 and has only two hits in his last 18 at-bats.

Notes: The Giants have been swept three times at home, by Oakland, the Chicago White Sox and Milwaukee. ... An MRI exam on Washington INF Aaron Boone 's injured left calf confirmed a strain that hasn't completely healed. He's been out since July 7. The exam was performed by Giants orthopedist Ken Akizuki, who recommended continued treatment and rest. ... After the game, the Nationals activated CF Lastings Milledge (strained right groin) from the disabled list and designated C Johnny Estrada for assignment. ''It's sad to see. I have a career day as far as a complete game and it makes him leave the ballclub,'' Redding said. ... Indicted home run king Barry Bonds was nowhere to be seen in these parts on his 44th birthday.