The Cubs find themselves in first place in the National League Central after three weeks of the season, but they're still not sure how good they really are.

They might be about to find out as they step outside the comfort of what some consider baseball's weakest division to host the New York Mets and then go to surging World Series loser Colorado.

"The Mets are a good team, and they've been playing good baseball," Cubs manager Lou Piniella said. "We'll get a good test here."

Certainly a better test than the Pirates gave them Sunday in a 13-6 rout. Combined with Saturday's 13-1 victory, it was the first time the Cubs have scored that many runs in consecutive games since 2003.

The facts are that half the Cubs' 12 wins have come against their personal pin-cushion Pirates, and 11 of the 12 against the Central. They're 1-2 against East contender Philadelphia.

The Cardinals, who just relinquished the Central's top spot to the Cubs, are already 8-5 outside the division. Milwaukee is 5-1.

So the next five games become very important for the Cubs.

"I didn't realize we were in first place, but early in the year you just want to win baseball games and win series," Piniella said. "I don't really look at the standings early. As long as we're playing good baseball and we're winning our share of games, good things happen."

The Cubs are winning for sure, as in four of the last five series. And they are 9-1 in series against the Central dating to last September.

They have swept the Pirates twice already. Sunday's game was over early and decided by the top two hitters in the lineup, Reed Johnson and Ryan Theriot.

"You always see when guys get a few hits, especially early on in the game, everybody follows suit," Theriot said.

Johnson and Theriot were on base eight times and scored six runs, with Theriot going 4-for-5 and raising his average to .481 on the homestand. Johnson, in his second day as leadoff hitter, appears to like his new home: He is hitting .400 at Wrigley Field this season.

Every position player had at least one hit for the Cubs, including Aramis Ramirez, who went into the game hitting .234 but came out at .275 with four hits, including his fourth homer.

"I feel pretty good at the plate, but I can't say I'm right where I want to be," Ramirez said. "I only had one good day."

As for the pounding given his old team in Pittsburgh, Ramirez said: "You've got to beat the teams you're supposed to beat. If they beat us, everybody would be all over us."

The Cubs don't meet the Pirates again until May 16-18. In the meantime, they have the Mets, Rockies, Cardinals, Brewers, Diamondbacks and Padres, which should give them an idea of how good they really are.

"It always feels good to be in first place," winning pitcher Ryan Dempster (3-0) said. "We've been playing a lot better. We've been swinging the bats unbelievably.

"It feels good to get to first place. Now the tough part is to try to stay there."

dvandyck@tribune.com