NEW YORK – The New York Mets spent most of the afternoon resting up for the Subway Series. Then in one sudden burst, they went rushing into their biggest rivalry.

Carlos Delgado’s two-run single capped a five-run rally in the bottom of the ninth inning and set off a wild celebration at home plate, and the Mets startled the Chicago Cubs 6-5 Thursday.

“This is going to give us great momentum going into the weekend,” Delgado said.

Manager Willie Randolph started a makeshift lineup because the Mets’ rain-delayed, 8-1 win Wednesday night ended at 12:53 a.m. David Wright, Carlos Beltran and Jose Reyes were among those scheduled to have a day off.

Instead, Wright and Beltran contributed as pinch-hitters and the Mets, boosted by key hits from Carlos Gomez, Ruben Gotay and David Newhan, pulled off their biggest ninth-inning comeback since 1999.

“Nice job by my A-minus boys” Randolph said.

Delgado’s one-out single gave the Mets a final thrill – and their seventh win in nine games – going into Friday night’s opener against the New York Yankees at Shea Stadium.

Cubs manager Lou Piniella watched relievers Ryan Dempster (1-2) and Scott Eyre blow the big lead. They lost for the sixth time in eight games, and headed back to Wrigley Field to play the Chicago White Sox on Friday.

“I just lost the game. There’s not much to say,” Dempster said. “It’s tough for the other guys to clean up my garbage.”

The Mets did little for eight innings and, with 48-year-old Julio Franco drawing big cheers for making easy plays at third base, the game took on a spring-training feel. Center fielder Endy Chavez lost track of the outs after catching a fly ball and Newhan threw away a routine grounder to second base.

That all changed in the ninth.

Down 5-1, the Mets got going when Newhan led off with a single and Gomez singled with one out. Piniella went to the mound to lecture Dempster, who loaded the bases with a walk to Beltran.

Chavez drew a walk that forced home a run, and Gotay’s RBI single brought Eyre from the bullpen. Wright batted for Shawn Green and hit a single that made it 5-4.

“The guys were not trying to win the game with one swing,” Wright said. “Especially after you have a couple of good at-bats early in the inning, the energy level goes up. Nobody wanted to make those last two outs.”

Delgado, who grounded into a double play earlier, did better this time with a grounder just beyond the reach of diving second baseman Ryan Theriot. As the ball rolled into right field, The Mets spilled from the dugout to embrace Delgado and everyone else who contributed to the stunning comeback.

The previous time the Mets overcame a four-run deficit in the ninth to win was May 23, 1999, when they scored five times off Curt Schilling to beat Philadelphia 5-4, according to the Elias Sports Bureau.

“I’ll tell you the truth, these guys have to do it. I don’t know what else to say,” Piniella said.

Ambiorix Burgos (1-0) won in relief.

Until the end, Chicago’s Angel Guzman had been in position for his first big league win. He had been 0-6 in 21 previous appearances in the majors, including 12 starts.

Guzman gave up one run and six hits in five innings. He tweaked his hamstrings while batting in the sixth and left the game.

Aramis Ramirez homered and drove in three runs for the Cubs.

In the fourth, Ramirez got an RBI single on a liner that hit halfway up the left-field wall. The ball hooked into the corner and Ramirez stood at the plate, apparently thinking it would either be foul or a home run.

Ramirez left no doubt with a two-run drive in the sixth for his 10th homer. He and Alfonso Soriano enjoyed a laugh on their way back to the dugout.

Former Mets minor leaguer Angel Pagan also hit a two-run homer in the sixth off Jason Vargas.

Vargas was called up from Triple-A New Orleans early Thursday when outfielder Moises Alou was put on the 15-day disabled list because of a strained left quadriceps.

Vargas, who began last year in Florida’s rotation, was 2-3 with a 5.30 ERA in the minors this season. He got this start after Mike Pelfrey was sent down with an 0-5 record.

New York’s first run came on Green’s RBI single in the fifth. The Mets missed a chance to get more when Delgado grounded into an inning-ending double play with runners at the corners.