SAN FRANCISCO -- With the Cubs reeling after the White Sox swept them, Mark DeRosa showed Monday why citizens of Wrigleyville are so optimistic about this season.

Aramis Ramirez (family matter), Alfonso Soriano (broken left hand) and Reed Johnson (back spasms) were all unavailable in the series opener against the Giants, so DeRosa grabbed the reins for the night, tallying two home runs and six RBIs.

It's been that way all season for the National League-leading Cubs: different guys stepping up on different nights.

Halfway through the year, there's yet to be a hole too big to fill. DeRosa, for one, has been an invaluable piece of the ever-changing puzzle.

He's played at five different positions. He's been up and down in the lineup. Anywhere Chicago manager Lou Piniella tells him to go, he goes.

"We've had a lot of injuries, and guys have been thrust into different positions," DeRosa said. "You really got to check your ego at the door and do whatever is needed to help out."

For DeRosa, it seems, that means polishing his power stroke. Before 2008, the right-hander had 48 home runs in 10 seasons. In just 78 games this year, he's got 10 -- the total he had in 149 games in 2007.

That's valuable regardless of the situation. But even more so now because Soriano (broken hand, strained right calf) has played just 51 games and isn't expected back until after the All-Star break.

"I'd like to think that as I play more, I learn my swing better and figure out how pitchers will attack me," DeRosa said. "We're all kind of realizing that we shouldn't just be waiting for that two-run bomb that we've been used to getting.

"That's forced everyone to bear down and have better at-bats."

Center fielder Reed Johnson (back spasms), whose trip to the disabled list has forced Jim Edmonds into everyday action, echoed DeRosa.

Out since mid-June, Johnson said it's important that different players are capable of fulfilling different roles. That's the difference between a good team and a great team, Johnson said.

"That's something great we've had this entire year," said Johnson, who'll return to action Thursday. "When guys have gone down, other guys have helped us back up. That's different than any other team I've played on."