Bruce Bochy has yet to announce his postseason rotation, but if Zito continues to pitch like he has over the past few weeks, a playoff start seems probable.
In the Giants' final home game before the NL division series, Zito looks to win four consecutive starts for the first time in six years in Thursday's finale with an Arizona Diamondbacks team on the verge of being eliminated from postseason contention.
With the NL West title locked up and little chance of catching the NL's other two division champions, San Francisco's biggest priority over the next week is getting its postseason roster ironed out.
The Giants (90-65), winners of 11 of 14, will decide Thursday if they'll add the suspended Melky Cabrera to the postseason roster, and a decision will eventually need to be made on the rotation. Bochy has said all five of his starters will be on the roster, but it's unlikely they'll all start.
Just making the postseason roster is a positive for Zito (13-8, 4.18 ERA), but getting a start seems likely given the Giants have won the last nine times he's taken the ball.
The left-hander has five victories in that stretch, and also a 1.45 ERA in winning his last three starts. The 2002 AL Cy Young Award winner, who hasn't lost since Aug. 2, hasn't won four starts in a row since reeling off five straight in 2006, his last season with Oakland.
"It's nice to be able to go out there and have fun and be loose in September,'' Zito said after allowing two runs in 5 2-3 innings against Colorado last Thursday. "When you have fun, you're relaxed, good things happen.''
Prior to facing the Rockies, Zito gave up one run over 6 2-3 innings in a 3-2 win in Arizona on Sept. 15. He is 3-0 with a 3.65 ERA in four starts versus the Diamondbacks (78-77) this season, with the Giants winning each.
San Francisco has just four wins in its other 13 games against Arizona, with one of those victories coming with Wednesday's 6-0 final. Pablo Sandoval singled twice and drove in two runs, while Marco Scutaro extended his career-best hitting streak to 14 games.
Scutaro, acquired from Colorado on July 27, is batting .466 during his run, and is hitting .441 in eight games against the Diamondbacks with San Francisco.
"We did clinch the other day, but we still have a job to do," said Brandon Belt, who is 5 for 8 in his last three games. "We want to gain momentum going into the playoffs."
The playoffs are just about out of the conversation for the Diamondbacks, who trail St. Louis by 5 1/2 games for the NL's second wild-card spot with seven to play.
Paul Goldschmidt, who is batting .344 with 11 RBIs during a nine-game hitting streak, is 2 for 10 with a pair of doubles off Zito.
The Diamondbacks counter with Patrick Corbin (6-7, 4.36), who'll be facing San Francisco for the third time this month.
Corbin has a 1.80 ERA in winning his two home starts against the Giants this year, but gave up four runs in five innings at AT&T Park on Sept. 3.
After yielding two runs in a season-best eight innings in a victory over San Francisco on Sept. 16, the lefty struggled in Saturday's 8-7 win in Colorado, permitting five runs in three innings, his shortest outing of his 15 starts.