PHOENIX -- Brandon Webb hit a two-run double and improved to 5-0 as the Arizona Diamondbacks defeated San Francisco 5-4 on Tuesday night.

Webb, off to the best start of his career, beat San Francisco's Barry Zito (0-5) for the second time in six days. Webb's five victories match the total of the Giants' rotation. He allowed three runs and nine hits in six innings. He walked two and struck out a season-high seven.

Webb spotted the Giants a 3-0 lead. But he hit a two-run double in the fourth -- his second two-run hit off Zito this season -- to give the Diamondbacks a 4-3 lead.

At 15-5, Arizona leads the NL West by six games, a bigger margin than it had at any point en route to the division title last year.

Brandon Lyon pitched the ninth for his fifth save in seven chances.

Fred Lewis had three hits and two RBIs for San Francisco.

The last time Webb faced the Giants, on April 16, he allowed only three hits in eight innings. It took San Francisco four batters to match that total Tuesday night.

Lewis led off with a single, took third on Ray Durham's single and scored on Randy Winn's sacrifice fly to give the Giants a quick 1-0 lead.

The Giants made it 3-0 in the second on RBI singles by Lewis and Winn.

In Zito's first four starts, his biggest lead had been one run, and it lasted less than an inning.

This time, his lead lasted less than three innings. Arizona cut it to 3-2 in the second on a two-run single by Chris Snyder, his sixth hit in 10 at-bats against Zito.

In the fourth, Mark Reynolds led off with a single and Justin Upton walked. Zito got the next two batters to bring up Webb, who hit Zito's first pitch into the gap in left-center field and give the Diamondbacks a 4-3 lead.

Webb's only other hit and RBIs of the season had come against Zito last week.

Webb scored on Eric Byrnes' single to put the Diamondbacks ahead 5-3.

Zito gave up five runs and six hits in 3 2-3 innings, his shortest outing. He walked three and struck out two.

San Francisco cut the lead to 5-4 in the eighth on Lewis' double off Tony Pena. Pena struck out Winn looking on fastball over the inside corner to strand the potential tying run at third.