CHICAGO -- Jon Lester did not want to leave Monday's game for the Cubs -- not with Wrigley Field packed for the home opener, the bullpen thin on available pitchers and the team trying to turn the recent road trip into a distant memory.

When a left hamstring issue was bothering Lester in the third inning of the 10-0 romp over the Pirates, the veteran lefty initially convinced manager Joe Maddon to leave him on the mound. Following a few more errant pitches and a delivery that just did not look right, Maddon pulled the plug on Lester's afternoon, though not before the starter's teammates took notice of his resolve.

"We respect that," Cubs shortstop Javier Baez said. "There's a reason he's out there. Hopefully it's not that serious."

The Cubs will have more information on Wednesday, following more tests on Lester's leg during Tuesday's scheduled team off-day. Right now, though, the injury does not seem serious. Lester tweaked his left hamstring while running the bases during a six-run rally in the second inning, during which he drove in a run with a hustle double and scored from second on a Ben Zobrist single.

Sitting in the Cubs' press-conference room following Monday's victory, Lester noted that he never felt a pop and did not feel anything he would describe as pain. What the pitcher felt was more like a cramp, but Maddon was not going to risk leaving Lester out there any longer.

And just as Lester lobbied to keep pitching, he is already planning on staying on schedule.

"In my mind, I'm making my next start," Lester said. "Tomorrow may tell us something different and then we'll re-evaluate, but I don't think it's as bad. Everybody on the training side always kind of thinks the worst-case scenario. I don't. I don't feel that way."

As things stand, the next man up for the rotation would be right-hander Tyler Chatwood , who is currently in the bullpen. Lefty Mike Montgomery would typically fill that spot, but he is on the 10-day injured list with a left lat issue and is not eligible to return until Monday. The way things line up, the Cubs would need a starter for Sunday's game against the Angels, if Lester is unable to go.

"I'm just ready to pitch whenever," Chatwood said. "Hopefully he's OK. He's our horse. We need him."

Maddon did not sound as optimistic as Lester.

"When you go in an MRI tube, normally it's going to delay things a bit coming back," Maddon said. "So we'll have to figure out who's going to start next."

In the bottom of the second, Lester came through with a two-out, two-strike double off Bucs starter Jameson Taillon. The Cubs starter slid into second base while Daniel Descalso scored Chicago's first run of the day. One batter later, Lester crossed the plate on Zobrist's single, sliding into home and getting up gingerly. Jason Heyward, who also scored on Zobrist's hit, put an arm around the pitcher to see if he was OK.

Lester said he felt a pull in his hamstring while running around third base -- not on either slide.

Lester took the mound for the third and promptly allowed a leadoff single to pinch-hitter Steven Brault. After his first two pitches sailed up and in to Adam Frazier, Maddon and head athletic trainer P.J. Mainville checked on the lefty. Lester remained in the game for three more pitches, giving up a single to Frazier before being pulled from the game for Brad Brach.

"He did talk me into [leaving him in]," Maddon said, "because I'm really deferring to his veteranship right there. It could've been a cramp -- I don't know. But, watching him throw the next pitch, the next hit, I didn't like it at all. The worst scenario would've been to leave him out there, work through it, get hurt worse and then bring the bullpen in."

Lester logged just 45 pitches and ended with two shutout innings, lowering his season ERA to 2.57 through three starts (14 innings). Two of Chicago's three victories through 10 games have come on days Lester started, including Opening Day in Texas. While the Cubs' pitching staff has labored, their rotation leader has been one of the few stabilizing forces out of the gates.

"His presence around here rubs off on a lot of people," Chatwood said. "I think the three best games we've played have been with him starting. I think everybody's locked in when he's out there. That's just the kind of person that he is."