SAN FRANCISCO -- Because he pitched well against the White Sox last weekend and St. Louis has a lineup that struggles against left-handers, Sean Marshall will get another crack at the starting rotation this weekend when the Cubs play the Cardinals.

Before Tuesday's game against the Giants, Cubs manager Lou Piniella announced Marshall would start in St. Louis either Saturday or Sunday, instead of pitching from the bullpen as the skipper originally said on Monday afternoon.

"I think that's the way we're going to go," said Piniella, who hasn't decided whether Marshall or Ted Lilly will toe the mound on Saturday. "We can decide after the day off on Monday how we go into the [All-Star] break."

Marshall mostly started in his first two years in the Majors, but he's pitched out of the bullpen for the majority of 2008. In 13 appearances this year out of the 'pen, Marshall has a 4.15 ERA in 8 2/3 innings.

Because of injuries to pitchers in the rotation, though, Marshall has made two starts in the past week. He was up and down -- four runs in 4 2/3 against Baltimore and three runs in seven innings at U.S. Cellular Field.

"Marshall threw the ball really well against the White Sox the other day," Piniella said. "You look at the Cardinals, and they're 11 games over against right-handers and one game over against lefties. That leads me to believe that we have a better chance with left-handers."

Marshall would prefer to continue starting, something he proved capable of doing in 2007 when he maintained a 3.92 ERA in 21 appearances (19 starts). But should the club ask him to return to the 'pen, he'd have no complaints.

"I'd rather do whatever they want me to do, so long as it lets me help this club here," Marshall said. "It really doesn't matter, I just want to help this team win games."

The left-hander said he feels more comfortable in the rotation, and he thinks he's proven himself as a Major League-quality starter.

Piniella, too, thinks Marshall has what it takes to avoid the reliever tag. He said Marshall has a good fastball, as well as the necessary fortitude to succeed at a high level. Marshall does, however, need to work on keeping his breaking ball lower in the zone.

As a starter in 2007, Marshall was a roller coaster. He threw six-plus innings while allowing two or less runs on nine occasions. But he also lasted fewer then four innings four times, including his last two turns.

"I think this kid is going to continue to improve," Piniella said. "I think he'll be a really good starter at the Major League level."