(Best E Casino) - A battle of left-handers will be on tap this afternoon, when Randy Johnson leads the NL West-leading Arizona Diamondbacks in the finale of a three-game series against Barry Zito and the San Francisco Giants from AT&T Park.

The 44-year-old Johnson is 3-0 with a 2.33 earned run average over his last three starts since going 0-6 in eight previous trips to the hill -- all Arizona losses. He last toed the rubber on July 21 against the very familiar Chicago Cubs, tossing seven shutout innings of two-hit ball to improve to 13-0 with a microscopic 1.84 ERA in 14 career games versus the Cubs.

Johnson has posted two no-decisions -- both Arizona defeats -- in the 2008 series with San Francisco. In 22 career starts against the Giants, the veteran southpaw is 7-8 with a 3.38 ERA.

Arizona remained one game ahead of the Los Angeles Dodgers in the division standings following Saturday's 5-3 triumph over the Giants. Ace Brandon Webb tossed seven strong innings and allowed three runs on four hits while striking out eight and walking two for the D'Backs, winners in four of five contests.

Chris Snyder went 2-for-4 with a pair of runs batted in for Arizona.

Giants stud pitcher Tim Lincecum didn't earn a decision after he allowed two runs on seven hits in seven frames. He set a new career high in strikeouts with 13 for the Giants, who have lost two straight after a three-game winning streak. Reliever Tyler Walker was touched for three runs -- one earned -- in one-third of an inning to absorb the loss.

Aaron Rowand went 2-for-4 with two RBI for the Giants, while Randy Winn knocked in a run and scored a run.

Zito is unbeaten over his last three outings (2-0) and defeated Washington on July 22, permitting three runs in six innings of a 6-3 victory. The lefty improved to 5-12 with a 5.56 ERA in 20 starts this season.

The USC product, who is 2-8 in 11 home starts in 2008, owns a 2-5 record and a 3.88 earned run average in eight career appearances against the Diamondbacks.

Arizona leads the 2008 season series with San Francisco by a 6-4 count.