PHILADELPHIA -- Dave Roberts could rejoin the Giants' lineup as early as Thursday, fulfilling his hopes for an accelerated comeback from arthroscopic left elbow surgery.

Roberts, who underwent surgery on May 11, initially was expected to miss six weeks. But he has been hitting and throwing without complications, and is expected to go on a brief injury rehabilitation assignment this week before being activated.

To get enough at-bats to regain his timing, Roberts might have to hopscotch among the Giants' extended Spring Training club in Scottsdale, Ariz., Triple-A Fresno or Class A San Jose, due to scheduled days off for those respective teams.

Manager Bruce Bochy said that if Roberts isn't activated on Thursday, when the Giants play their series finale at Arizona, he should be ready for the weekend Interleague series against Oakland.

"The sooner the better, for sure," Roberts said Sunday.

Once Roberts returns, he expects to resume being the effective leadoff hitter the Giants expected when they signed him to a three-year, $18 million contract last offseason. Roberts acknowledged that the bone spur and floating bone chips in his elbow hampered his early-season performance and that he's "definitely not" the player who hit .216 with a .283 on-base percentage.

With Roberts back, Randy Winn will return to right field and move from the leadoff spot to second or third in the batting order.

"It adds another dimension," Bochy said, pointing out that Roberts and Winn will give the Giants two hitters with speed and on-base potential at the top of the lineup.

The Giants also will face a decision regarding whether to send Daniel Ortmeier or Fred Lewis back to Triple-A Fresno. Ortmeier (.275, one home run, four RBIs entering Sunday) switch-hits and is the better outfielder, but Lewis (.268, two homers, 12 RBIs) has generated more offense and is faster.

Happy returns: Ryan Klesko, who missed five games in a row with a sore back, returned to the lineup at first base.

"The way he was swinging, it's good to have him back," Bochy said, referring to Klesko's .339 average (21-for-62) in his previous 22 games.

With production like that, playing Klesko every day might make sense. But Klesko will turn 36 on June 12, and, like many Giants, must be handled with care.

"At this stage in his career, he needs [an occasional] day off, too. There's times that his back will flare up," Bochy said, referring to Klesko's "violent" swing that makes chiropractors wince. "If he gets his needed days, you're going to get more production out of him."

Getting in there: Steady activity benefited Kevin Frandsen, who started five of the previous six games. Filling in four times for second baseman Ray Durham and once for shortstop Omar Vizquel, Frandsen looked sharp defensively.

Frandsen said that due to his sporadic activity in previous stints with the Giants, "I always felt like I was a step slow, two steps slow in the field. Now I can show what I can do with my range."

Frandsen also gradually found an offensive groove, shown by his 2-for-4 effort with a home run and a double Saturday off Phillies ace Cole Hamels. "It was a night when things started to fall," Frandsen said. "I've been hitting the ball hard for three weeks."

Repeat effort: Winn's leadoff home run Sunday off Philadelphia right-hander Freddy Garcia was his second in six games. He also hit one last Tuesday at New York in the road trip's opener. This was Winn's 13th career leadoff homer and eighth as a Giants hitter. It wasn't entirely a surprise, since Winn entered the game with a .375 career average (9-for-24) against Garcia.

Coming up: The Giants conclude their series against Philadelphia with a 10:05 a.m. PT start on Tuesday. Barry Zito (5-5), 2-0 with an 0.64 ERA in his last two starts, will oppose Jon Lieber (2-3), who allowed four runs in six innings in a 9-4 loss May 5 at San Francisco.