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What figured to be a promising homestand for the Pittsburgh Pirates has become a major disappointment. Now, the Pirates must hope their playoff hopes aren't headed in the same direction.

They'll look to avoid a three-game sweep -- their first at home all season -- Sunday against the Chicago Cubs.

The Cubs won 4-3 on Saturday, as Jeff Samardzija pitched a four-hitter in his final start of the season and David DeJesus singled in Welington Castillo with the go-ahead run in the eighth.

"The guy over there, that's a special arm," Pirates manager Clint Hurdle said of Samardzija. "Tonight, we needed to find a way to dig one out of the dirt, and we weren't able to do that."

The Pirates (72-66) have dropped six of eight overall and three of five on their homestand against Chicago and Houston, the owners of the two worst records in the NL.

Andrew McCutchen's struggles continued Saturday as he was held hitless for a third straight game while striking out three times. Neil Walker missed his 11th consecutive game with lower back tightness.

Despite their recent struggles, the Pirates still are only 1 1/2 games behind St. Louis for the second NL wild card. They will try to bounce back Sunday and keep the Cubs (53-86) from completing a three-game road sweep for the first time in 2012. Chicago had lost 17 of 18 away from home before taking the first two games this weekend.

Alfonso Soriano, who homered Saturday after driving in three runs Friday, is hitting .350 with three homers and nine RBIs in 10 games against Pittsburgh this year.

The Pirates will hand the ball to Jeff Locke (0-1, 4.82 ERA), who will make his second straight start after replacing Erik Bedard in the rotation earlier this week.

Locke struck out six but gave up five runs -- three on a homer -- in five innings of a 5-1 loss to Houston on Monday.

"He did pitch well," Hurdle told the Pirates' official website. "He used his fastball very well, he changed speeds. He should walk away knowing he did some good things out there."

The left-hander will be making his first appearance against the Cubs.

Chris Rusin (0-2, 9.00) will make his third career start for Chicago as he tries to bounce back from an ugly one earlier this week.

Rusin, who gave up one run and one hit in five innings of a loss to Milwaukee on Aug. 21, was recalled from Double-A Tennessee before Tuesday's game at Washington. The left-hander was pulled after the first four batters reached in the second. He allowed five runs and eight hits -- two homers -- in the 11-5 loss.

"Hopefully I'll learn from my mistakes and bounce back next time," he said.