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CHICAGO -- Shortly before rain postponed Sunday's game between the Cubs and the Pittsburgh Pirates, Chicago manager Lou Piniella was given some encouraging news: His starting rotation may be healthy for the stretch run.

Piniella has endured a season where he had to go stints with one his four top starters sidelined. Rich Harden and Ryan Dempster have spent time on the disabled list, while Ted Lilly is scheduled to be activated from the DL for his start Monday at San Diego.

And on Sunday Piniella got news that right-hander Carlos Zambrano should be ready to rejoin the team Aug. 25 for a start against the Nationals. he's been out because of back spasms.

"Over a period of six weeks we lost all three starters, it just so happened it was our No. 1, No. 2 and No.3. So we're starting to get the pieces back and hopefully Lilly and Zambrano get our rotation back and we'll play much better," Piniella said. "You need pitching, too."

The game was called after a delay of 3 hours, 15 minutes. No make up date was announced.

Harden, who was scheduled to start Sunday, will be pushed back to at least Thursday when the Cubs start a four-game series against the Dodgers in Los Angeles. The Cubs will stick with their scheduled rotation for a three-game series at San Diego. Lilly will start in the opener on Monday followed by Dempster and Randy Wells.

Pirates scheduled starter Ross Ohlendorf will be pushed back to Tuesday against Milwaukee and Kevin Hart will make his scheduled start on Monday.

The Pirates, who have lost 12 of 13 games since winning back-to-back games against the Nationals on July 31 and Aug. 1, got an unexpected day off.

Hart said the Pirates need to take advantage of playing on the big league level and improving on their overall play.

"Go out every day and try to get better. I think that's our main goal," Hart said. "I think we have a lot of guys that have an opportunity to get a ton of experience at this level. I think it's going to benefit us the more we have guys that can get out there and get used to playing here and get used to playing at this level and get comfortable.

"I think we should improve as much as we can this year and next year come out and be ready to roll," Hart said.

Piniella said that his rotation might benefit in September from the injuries and the added depth of Tom Gorzelanny who is 2-1 since joining the Cubs.

"Look, Dempster has a fresh arm. He missed three weeks. Lilly has missed three weeks so he is going to have a fresh arm," Piniella said. Look at it from that perspective and the other good thing is we have six starters here with Gorzelanny so if there is a little bit of a problem at least we are covered from that standpoint."

Game notes

Cubs SS Ryan Theriot stayed home Sunday with the flu. Piniella said Theriot will not fly with the team to San Diego on Sunday. Piniella expects him to fly to San Diego on Monday, but doesn't expect him in the lineup. ... LF Alfonso Soriano, in a 2-for-20 slump, was scheduled for the day off on Sunday.