PITTSBURGH, SEPT. 27 -- The Pittsburgh Pirates of May, June and July raced to the top of the National League East with a flashy offense that covered for a patchwork pitching staff. The Pirates of August and September have stayed in first place because of a suddenly stable starting rotation that has become stingy during the stretch drive.

Rookie left-hander Randy Tomlin provided another in a series of solid outings by Pittsburgh starters tonight, and the Pirates completed a three-game sweep of the Chicago Cubs with a 3-2 victory before 25,049 at Three Rivers Stadium.

Pittsburgh (91-65) won its fourth consecutive game and seventh in eight contests to maintain a three-game lead over the New York Mets -- who also won -- in the NL East with six to play. The Pirates reduced their magic number for their first division title in 11 years to four.

They departed late tonight for St. Louis, where they'll play the Cardinals for three games and hope to clinch before the Mets -- who have won three straight but have gained no ground -- arrive here Monday for the season's final series.

"We've just got to keep winning," Pittsburgh Manager Jim Leyland said, "because it appears the Mets are not going to lose. . . . We didn't expect this final stretch to be easy, and those expectations are proving correct."

The Cubs, meanwhile, headed to New York, part of 13 consecutive contests against the Pirates and Mets. Chicago is 3-7 thus far in that stretch, including 1-5 against Pittsburgh. The Pirates finished the season series with 14 wins in 18 meetings with Chicago, and their victory tonight -- like those of the past two evenings -- was by comeback.

"If we're any barometer, the Pirates certainly deserve to be the champs," Cubs second baseman Ryne Sandberg said. "Of course, if you just judged by the games we've played against them, I guess you'd think they were the greatest team of all time."

Tomlin rebounded from a sluggish beginning to craft a seven-inning, five-hit, two-run performance. The Pirates rebounded from a quick 2-0 deficit with runs in the first, third and sixth innings. The winning score came on Sid Bream's two-out flare on a defensive, two-strike swing for an RBI double. Reliever Vicente Palacios got the final six outs for his third save.

But the storyline, as it has been, was Pittsburgh's starting pitching. In his 11th major league start, Tomlin, 24, extended a run of proficiency in which Pirates starters are 5-1 with a 1.91 ERA in the past six games.

"Our pitchers are doing a great job for us in pressure situations," Bream said. "They're keeping us in games, taking some of the heat off the offense. We haven't been scoring as quickly or as much, but we know we don't have to. . . . Hitting goes in streaks, but good pitching is a constant -- and we've had that."

Tomlin (4-4) quietly has become a crucial member of the Pirates' rotation. With Zane Smith, he has given Pittsburgh two dependable left-handers. Before last month it had only the erratic John Smiley and Neal Heaton to go with righties Doug Drabek and Bob Walk.

"It's an incredible luxury to have all these lefties around," Leyland said. "Every team in the league is desperate for left-handed pitching, and we have a surplus. . . . Zane Smith has gotten all the notoriety, and deservedly so, but this kid has given us a tremendous boost too."

Tomlin was promoted from Class AA Harrisburg (Pa.) Aug. 6 -- two days before the Pirates traded for Smith -- and beat the Philadelphia Phillies with a five-hitter in his major league debut that night. He has been steady since, having surrendered two earned runs or fewer in nine of his 11 big-league outings.

"This one was a struggle," said Tomlin, who lost his previous two starts. "I haven't been going real good the past two weeks, and you don't like to get behind right away like I did. . . . But I thought I hung in there and battled pretty well."

With one out in the first, Sandberg lifted a pop fly to shallow center field that fell between three Pirates for a double. Tomlin appeared to pick him off as Sandberg broke prematurely for third base, but the pitcher was called for a balk. Sandberg scored on Mark Grace's groundout, and Andre Dawson made it 2-0 by depositing a 3-2 fastball well beyond the left field wall for his 26th home run.

But Wally Backman led off Pittsburgh's half of the first by beating out a bunt and eventually scored on Bobby Bonilla's RBI single.

One-out doubles by Jay Bell and Andy Van Slyke -- who's hitting .383 with 14 RBI in his last 13 games -- against Mike Bielecki (7-11) in the third tied the game at 2.

The tie-breaking run came three innings later, after Bonilla laced a one-out, ground-rule double to the right field corner. One out later Bream fought off a tough, two-strike fastball from Bielecki to deliver his game-winner and give him 11 hits in his last 18 at-bats.