The San Francisco Giants swept the Washington Nationals while making a case for a new baseball axiom: The fifth inning is a good time to pick on a rent-a-pitcher from the minors.

For the second straight day, the Giants came alive in the fifth against a starter making a one-game visit from Triple-A Columbus. Consecutive hits by Ray Durham, Randy Winn and Bengie Molina chased Tyler Clippard from San Francisco's 3-2 victory Monday night.

Matt Cain (3-4) allowed one run and eight hits over 6 1-3 innings to get his first victory since May 13 for the Giants, who outscored the Nationals by a combined 22-4 to complete their first four-game sweep of the franchise since 1994 _ more than a decade before the team moved from Montreal to Washington.

San Francisco has won six of eight overall, and its seven-game road winning streak is its longest since 2003.

On Sunday, the Giants used a four-run fifth to chase Garrett Mock, who was making his major league debut because of an injury to Odalis Perez. Mock was optioned back to Columbus after the game and replaced by Clippard, who filled a hole in the rotation created by an unexpected doubleheader late last week.

Clippard (0-1), whose previous big league experience was a 3-1 record in six starts for the New York Yankees last year, allowed three runs and five hits with four walks and six strikeouts in 4 1-3 innings in his Nationals debut. He was holding his own in a 1-1 game until Durham doubled to the right field corner with one out in the fifth.

Winn then fouled off four consecutive pitches before hitting a changeup through the middle to score Durham, his second RBI of the game. Molina then doubled to the wall in left to score Winn, giving the Giants a 3-1 lead _ enough to beat the worst hitting team in the league.

The Nationals have lost eight of nine, scoring three runs or fewer in all the losses. They suffered the ignominy of having two runners caught stealing in the first inning; Elijah Dukes and Lastings Milledge were both thrown out trying to swipe second.

Washington's only runs came on a sacrifice fly by Jesus Flores in the fourth and a throwing error by catcher Molina in the eighth. Cain worked out of a one-out, first-and-third jam in the sixth by striking out Flores, who fouled off five pitches and worked a full count before whiffing on a slider.

Cain was replaced after hits by Felipe Lopez and Wily Mo Pena put runners on first and third with one out in the seventh, but reliever Keiichi Yabu got pinch-hitter Aaron Boone to hit into a double play.

Molina threw a wayward pickoff attempt toward in the eighth to allow Milledge to score from third. The Nationals loaded the bases with two outs later in the inning, but Brian Wilson entered and got Lopez to fly out.

Wilson finished for his 18th save.

Notes:@ The temperature was 92 degrees _ with high humidity _ at the 7:10 p.m. first pitch. Sunday's matinee was played in 94-degree heat. ... The Nationals, playing in a new ballpark, drew 26,209 to pass the one million mark for the season. They are averaging around 29,000 at Nationals Park, about 4,800 more than they averaged last year in their final season at RFK Stadium.