The Mets walked a tightrope for two weeks. A seven-game losing streak in late September put them dangerously close to a second straight late-season collapse and another year narrowly missing the playoffs.

Two games out of the lone Wild Card spot with three games left, those attempting to write the epitaph of the 1999 Mets were premature. New York swept the Pittsburgh Pirates at home. The Cincinnati Reds lost twice to the Milwaukee Brewers, creating a Monday night tie-breaker.

At the concrete bowl formerly known as Riverfront Stadium (renamed Cinergy Field), Al Leiter took the mound for the visiting Mets. He had helped end that seven-game skid by besting Greg Maddux and the Atlanta Braves, which up to this point had been his high point in a rather mediocre year. But Leiter proceeded to deliver the most significant outing of his major league life: a two-hit shutout to lift New York to its first postseason berth since 1988.

“Al has pitched a no-hitter,” manager Bobby Valentine said, referring to a night in 1996 with the Florida Marlins. “But I don’t know if he’s ever pitched a better game.”

Before he ever threw a pitch, Leiter had a lead. That came courtesy of Edgardo Alfonzo, capping a career season. Posting team hitting records for second basemen, “Fonzie” combined a .304 batting average and an on-base percentage of .385 with 27 homers and 108 RBI.

Home run No. 27 came early on in Cincinnati. After Rickey Henderson led off with a single, Alfonzo drilled the 1-0 pitch from Reds starter Steve Parris to center field. Jeffrey Hammonds went back…back…back…and then ran out of room. The fly ball carried its way over the fence and Alfonzo had one of what would be many crucial October hits as a Met.

Leiter overcame a wobbly beginning. He allowed a baserunner in each of the first three innings, but settled down and eventually retired 13 Reds in a row. He dotted the strike zone beautifully — striking out seven and rarely leading to much hard contact.

“I felt like I was leading by 10 runs, once I settled in,” he said. “I had a good curveball that night.”

Leiter’s cushion increased to five runs thanks to a third-inning bases-loaded walk, a fifth-inning homer from Henderson, and a double from Alfonzo in the top of the sixth.

When Cincinnati mounted a last-gasp threat, it was merely an effort to avoid the shutout. The Reds couldn’t even do that. The last batted ball, off Dmitri Young, fittingly found the glove of Alfonzo and put the finishing touches on Leiter’s 5-0 masterpiece.

The Mets were off to Arizona for more loops on their roller-coaster ride.