SAN FRANCISCO — The Washington Nationals might as well change their name to the Washington Generals, the storied club that always managed to lose to the Harlem Globetrotters.

The analogy works just fine for the Giants.

Matt Cain tossed a four-hit shutout, the second of his career, and Dave Roberts chopped single for a run in the eighth inning yesterday afternoon as the Giants won 1-0 to finish a season sweep of the lowly Nationals.

The Giants hadn't swept an opponent at home all season before taking three from the Nationals. They also swept four games in Washington, D.C., last month.

It was the second time in San Francisco franchise history that the Giants wiped out an opponent in a season series of seven games or more. They were 9-0 against the Florida Marlins in 1998.

Cain had a two-hitter through eight innings and Manager Bruce Bochy signaled his intention when he had the pitcher hit for himself in a scoreless game. Cain executed a sacrifice after Steve Holm led off the eighth with a single. Pinch runner Eugenio Velez scored from second base when Roberts tapped a 1-2 pitch over the mound and into center field.

The Giants were one of five teams in the major leagues that didn't have a complete game, but Cain gave himself a chance by being economical and not walking a batter through eight.

Giants Manager Bruce Bochy showed more confidence in Cain after he gave up an infield single to Willie Harris and a one-out double to Cristian Guzman in the ninth.

With National League saves leader Brian Wilson warm in the bullpen, Bochy strolled out and delivered a message to Cain but did not ask for the baseball.

Cain got Ryan Zimmerman to fly out to shallow right field. Harris did not test Randy Winn's arm, and Cain pumped his fist after Austin Kearns lofted another fly out to right field to end it.

It was the first shutout by a Giants pitcher since Noah Lowry threw one Aug. 21 2006. Cain's only other shutout was a one-hitter against the A's in '06.