Two years after starting the San Francisco-based All-Star Game and finishing third in the Cy Young Award voting, Brad Penny signed with the Giants on Monday to be their No. 5 starter. His first assignment is expected to be Wednesday in Philadelphia.

If the Giants keep their rotation intact, Penny would face the first-place Dodgers on Sept. 13 in San Francisco and Sept. 19 in Los Angeles.

"He's still bringing it pretty good," said Bobby Evans, vice president of baseball operations, adding that the Giants considered signing Penny over the winter. "His last start was in and around 94 (mph). He's a veteran. He's been an All-Star. He's got experience. It's certainly an area where we have immediate needs, and he can possibly address those needs."

Penny, 31, cleared waivers Monday, and the Giants hurried to sign him - roughly $75,000, a prorated portion of the minimum salary - so he'd be eligible for the postseason roster. Anyone joining the organization in September is ineligible.

Technically, it's a minor-league deal, just so the Giants didn't need to remove someone from the 25-man roster before today, when roster limits increase to 40. He'd be added to the roster before Wednesday's start.

The Red Sox placed Penny on waivers last week. Had the Giants claimed him before he cleared, they'd be on the hook for the rest of his $5 million salary.

With the Red Sox, Penny was 7-8 with a 5.61 ERA. He was far better with the Dodgers, at least when he won 16 games in both 2006 and 2007. He sustained a shoulder injury last season and fell out of favor with the Dodgers and their management, his character becoming a sore point.

It's reportedly a reason the Rockies - whose manager, Jim Tracy, had Penny in 2005 in Los Angeles - didn't pursue him, despite losing Aaron Cook to an injury.

Penny didn't help his reputation last year. His request for a contract extension in spring training was declined, and he said the Dodgers didn't believe he was hurt and criticized the coaching staff, mentioning Larry Bowa by name, for not being supportive. The team severed ties with Penny before the season ended, and Bowa blasted him, saying he was lazy, out of shape, always late and refused to assist younger players.

"We've signed a player fully anticipating he's going to be an asset in every way," Evans said.

Penny is replacing Joe Martinez in the rotation after Martinez was optioned to Triple-A Fresno because of consecutive poor starts. The Giants pushed back Tim Lincecum (a season-high 127 pitches in his last start) to Thursday to give him extra rest, opening a spot Wednesday.

At this year's All-Star Game, Lincecum questioned whether extra help was necessary, considering it could alter the chemistry, saying, "We're really meshing well with the team we have."

Penny will be a free agent after the season.

E-mail John Shea at jshea@sfchronicle.com.

This article appeared on page B - 1 of the San Francisco Chronicle