The left-hander looks to help the Giants avoid a 10th consecutive home loss to the Miami Marlins on Saturday.
Grieving for his 84-year-old father, Joseph, who passed away in California on Wednesday, Zito (4-5, 4.67 ERA) won't veer from his schedule and remains in position to make this start.
"His routine will remain the same," manager Bruce Bochy told the Giants' official website. "There's nothing that's going to change, right now. He's scheduled to go."
Zito is 5-1 with a 2.45 ERA in eight starts against the Marlins.
However, he's 1-1 with a 4.18 ERA in his last four home starts after going 3-0 with an 0.55 ERA in his first five. He allowed two runs and struck out eight in 5 2-3 innings of a 5-3, 13-inning home loss to San Diego on Monday.
San Francisco (37-36) has lost 21 of 35 and fell for the fifth time in seven games, 6-3 to Miami on Friday.
Though the Marlins (24-49) own the majors' worst record, they've won eight of 13 overall and have outscored the Giants 34-16 during their remarkable nine-game winning streak at AT&T Park.
The Marlins can't put a finger on the reason for their success at San Francisco.
"I don't know, I'm a baseball player not a sociologist,'' Miami's Logan Morrison said.
Rookie outfielder Marcell Ozuna hit a go-ahead single in the eighth after tying it with a run-scoring single in the sixth Friday. He also threw out San Francisco's Andres Torres trying to stretch a sixth-inning double into a triple.
Morrison homered for the first time this season. He's batting .333 (9 for 27) with three RBIs in eight games since making his season debut June 9 from knee surgery.
Scheduled Miami starter Jacob Turner (1-0, 2.16) overcame six hits and three walks by yielding two runs on 96 pitches over five innings while not factoring in the decision of a 3-2 win at Arizona on Monday.
"Unfortunately, my pitch count was elevated quickly, but being able to limit them to two runs with all the baserunners they had was key for us," Turner told the Marlins' official website after making his fourth start since being called up May 31.
The right-hander is making his first appearance against the Giants, but likely won't face Torres after he injured his knee Friday.
San Francisco is already without third baseman Pablo Sandoval (foot) and outfielder Angel Pagan (hamstring), but hopes to have shortstop Brandon Crawford back after he missed the first two games of this set with two sprained fingers.
"It feels a little better, but not quite where I want it to be," Crawford said.
"It still doesn't feel good when I'm throwing,'' he said. 'I don't have much behind it.''
With three hits Friday, San Francisco's Gregor Blanco is batting .400 (22 for 55) in his last 16 games. He hitting .477 (21 for 44) in his last 12 against the Marlins.