CHICAGO -- The San Francisco Giants likely need a better performance from right-hander Johnny Cueto than they got in his last outing if they're going to split a four-game series with the Chicago Cubs on Sunday.

Cueto, a two-time All-Star, allowed four runs in 4 2/3 innings on Tuesday in a loss to the Arizona Diamondbacks in his shortest outing of the season for theGiants. He is 14-5 with a 2.98 ERA this year and 9-8 with a 3.34 ERA in 23 career starts against Chicago.

"I think the pitches caught up with him," Giants manager Bruce Bochy told reporters after that game. "His command was a little off, he started missing his spots. It just got away from him."

The Cubs (87-48), who lead the National League Central and own the best record in the majors, won the first two games of the series, 5-4 on Thursday and 2-1 on Friday. The Giants held off the Cubs 3-2 on Saturday behind Madison Bumgarner's 10-strikeout performance.

The victory in a playoff-like atmosphere in front of 41,250 fans boosted the Giants' spirits. They're just 16-29 since the All-Star break.

"It's a tough group," Bochy said. "Despite what happens, I really like the way they're coming out and staying focused. They've had their backs to the wall and been through difficult times. But they're going to keep fighting. Sure, we've had some issues in the second half, but it's all about going out there every day with the same effort."

The Giants (73-62) lead the National League wild-card standings but have won just five of their last 13.

"It was one we definitely wanted and needed," Giants catcher Buster Posey said about Saturday's win. "It was good to score some runs off (Jake) Arrieta and then for our bullpen to hold the lead the last three innings."

On Sunday, Cubs right-hander John Lackey (9-7, 3.41 ERA) is expected to make his first start since he went on the disabled list Aug. 15 with a right shoulder strain. He allowed an unearned run in 6 2/3 innings on Aug. 14 against the St. Louis Cardinals before he exited with the injury in his last start. He is 6-4 with a 2.47 ERA in 13 home starts.

Lackey is 1-1 with a 2.57 ERA in two regular-season career games against the Giants.

Cubs first baseman Anthony Rizzo and right fielder Jason Heyward were out of the starting lineup Saturday against left-hander Bumgarner but are expected back Sunday against Cueto.

Veteran reliever Joe Nathan could soon make his first appearance for the Giants, who drafted him in 1995 and purchased his contract fromDouble-A Richmond on Saturday. The Giants signed the 41-year-old as a free agent on Aug. 16 after the Cubs released him on Aug. 8. Nathan previously pitched for the Giants from 1999 to 2003 before he and left-hander Francisco Liriano were traded to the Minnesota Twins for catcher A.J. Pierzynski and cash in 2003.

"It made everything a lot more comfortable, a lot easier to come back here, a little less to have to kind of prove myself," Nathan said of returning to the Giants.

Nathan went 1-0 with a 0.00 ERA in three games with the Cubs.

"At that time, we just couldn't fit everybody in," Cubs manager Joe Maddon said. "He had one really good game up in Milwaukee where we got a couple guys on and he struck out the side. His pitches got up to the low 90s (mph) with some really good break."

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