Peavy was acquired from San Diego at the July 31 trade deadline. The right-hander has been on the disabled list since June 13 with a strained tendon in his right ankle and was struck on his pitching elbow during a rehab game on Aug. 24.

The 2007 NY Cy Young Award winner tossed between 50 and 60 pitches during his bullpen session before Chicago hosted the Boston Red Sox.

"Getting better," Peavy said. "I'd be lying if I told you I was out there completely normal, but nothing crazy. I'm able to get some extension."

Peavy said it was much improved from his last rehab start with Triple-A Charlotte on Aug. 29 when he had to leave after 3 1-3 innings because of elbow tightness. He said he was able to throw all his pitches during Sunday's session, even if he didn't turn it up all the way.

"Hopefully we're on the right track now without any setbacks," he said. "As crazy as this has been, who knows? I certainly would love to pitch soon."

Peavy said he probably will throw another bullpen session in a couple of days and go from there.