CHICAGO — For one brief moment, a smile crossed Aramis Ramirez's face when he learned the Chicago Cubs took the lead in the National League Central. Then, it disappeared.

The Cubs know how drastically fortunes can change, so they weren't about to jump for joy over moving into first place on Sunday.

Ramirez tied a career high with four hits, including a two-run homer, in a 13-6 victory over Pittsburgh that gave Chicago its second three-game sweep of the Pirates this season.

Then, he had a question: "Did St. Louis win today?"

No, the Cardinals lost to San Francisco, so the Cubs took a half-game lead in the Central. Ramirez let out a smile and then it was gone.

"We still got, what, 150 games to go?" he said.

Actually, they have 144. But if Ramirez wants to prolong this season, well, so do the rest of his teammates.

Chicago got big days from Ramirez and Ryan Theriot and won for the 11th time in 14 games. Theriot had four hits, scored three runs and drove in two. With Saturday's 13-1 drubbing, this was the first time the Cubs scored 13 or more in back-to-back games since they did it against Florida and Atlanta on July 20-21, 2003.

Chicago banged out a season-high 18 hits, the most since it had 20 against Cincinnati last August 16, while sending Pittsburgh to its fifth straight loss. The win was Chicago's ninth straight against the Pirates, matching the Cubs' longest win streak against them since Sept. 5, 1938 to May 13, 1939.

"It feels great to be in first place," starter Ryan Dempster said. "Now, the tough part is trying to stay there."

Dempster (3-0) wasn't feeling great after Pittsburgh scored three runs in the fifth to cut it to 5-3, but Chicago responded with five in the bottom half against reliever Franquelis Osoria. The Pirates committed two errors in the inning, and Ramirez capped the outburst with his fourth homer.

The four-hit game was Ramirez's 18th and his first since Sept. 27 at Florida.

"I felt pretty good," said Ramirez, who raised his average from .234 to .275. "I can't say I'm right where I want to be because I only had (one) good day."

At 12-6, the Cubs matched their best 18-game start since 2004. One reason is their patience at the plate. The Cubs walked seven times Sunday after drawing 10 the previous day.

Pittsburgh's Nate McLouth extended his hitting streak to 18 with a single in the first — the longest by a Pirate since Jason Kendall hit in 20 straight in 2004.