CINCINNATI >> The last time the Reds got off to such a good start, they ended up winning the World Series.

Chris Heisey drove in three runs, and the Reds used a patient approach at the plate to beat the Houston Astros 8-2 last night for their best start in 21 years.

At 4-0, they’re the only unbeaten team left in the National League. They hadn’t won their first four since 1990, when they opened 9-0 and went on to sweep Oakland for their last World Series championship.

“You get off to a good start and try to keep the momentum going and keep winning,” Heisey said. “I’ll say we’re probably going to lose a game before long, but if we go 162-0, we’ll be making some serious headlines.”

The defending NL Central champs showed a lot of confidence in their first four, playing up to a title that’s had a carry-over effect.

“Remember I said that whatever we sold last year was going to be an easier sell this year because of the results,” manager Dusty Baker said.

By contrast, the Astros fell to 0-4, the second year in a row they’ve foundered. They dropped the first eight games last season, burying themselves in the Central with a 17-34 start in April and May. Houston finished the season strong and wanted to avoid another discouraging beginning this time around.

Instead, they’ve been overwhelmed by two of the league’s top teams, dropping three in Philadelphia before heading to Cincinnati to face a team that’s been even better than last year in one way.

The Reds’ offense led the NL in most categories last season, including homers and slugging, but ranked 10th in walks. They’ve added patience to their approach this year, walking 18 times in their four wins.

Against J.A. Happ (0-1), they did the most damage by not even swinging.

Heisey walked with the bases loaded, was hit by a pitch with the bases loaded, and singled home a run off Happ, who helped the league’s top offense immensely with his early control problems.

“I don’t know if it was just a lack of aggressiveness at the outset,” said Happ, who lasted only four innings. “I felt I was around the (strike) zone. They definitely took some quality pitches.”

The left-hander repeatedly missed low with his pitches. He walked three in the first inning, including Heisey to force in a run. The Reds sent eight batters to the plate for three runs — Scott Rolen had an RBI single, and Heisey broke up a potential double play with a hard slide into second base, bringing home another.