MLB

ALEX POPS PAP IN 9TH

BOSTON – When Alex Rodriguez stepped in to face Jonathan Papelbon in the ninth inning last night at Fenway Park, he couldn’t have asked for worse conditions.

A driving rain was blowing into A-Rod’s face. Since landing on the front page of The Post on Wednesday for nothing to do with baseball, A-Rod at times looked confused. And when the Red Sox closer’s first two pitches resulted in strikes, to say things looked dim for Rodriguez wasn’t quite descriptive enough.

Two outs. Two strikes. And a stud closer on the mound.

Then Papelbon attempted to close out A-Rod with a fastball that the Yankees’ cleanup hitter drove through the rain and over the right-field wall for what proved to be the game-winning hit in a pulsating 6-5 Yankees win in front of 36,793 at Fenway Park.

“I thought it was a pretty good pitch,” A-Rod said of the heater that he swatted for his 20th homer. “At 0-2 you are battling for your life. You are just trying to stay in the at-bat and try not to do too much.”

Until stunning Papelbon and the sold-out crowd, A-Rod’s night consisted of an infield RBI single and popping up with runners on first and third and one out in the seventh.

“I have to get the job done,” A-Rod said of not delivering earlier. “In that situation it’s not acceptable. That run has to come in. I knew I would get another shot.”

A-Rod’s homer provided Mariano Rivera a save chance, but the margin of error was thinner than one run. Because Rivera had to go through David Ortiz, Manny Ramirez and Kevin Youkilis to protect the Yankees’ fourth win in the last six games against the Red Sox, who lead the Yankees by 12½ games in the AL East.

Rivera responded, getting Ortiz to end an 11-pitch at-bat with a liner to Bobby Abreu in right, fanning Ramirez with a 2-2 pitch, hitting Youkilis and fanning Mike Lowell to end it.

“It was very satisfying for us to win,” said Joe Torre, who removed Andy Pettitte in the fifth because of back spasms that surfaced in the third. “Coming in to face that part of the batting order, you know it’s not going to be easy.”

Pettitte, who missed time in spring training with back spasms, said he was upset he couldn’t finish the fifth.

“I just hated that I wasn’t able to get through the last inning,” said Pettitte, who said the chilly, rainy night may have contributed to his back problem.

Because the Yankees have never been this far out this late in the season under Joe Torre every game is examined.

But according to A-Rod, last night means nothing if the grind-it-out mentality evaporates in Chicago, where the Yankees open a four-game series tonight against the slumping White Sox.

“It’s important what we do after this,” A-Rod said. “We have to back it up.”

It might have been easier to start doing that tonight if Roger Clemens was on the hill instead of Matt DeSalvo. And Tyler Clippard goes tomorrow night. But nothing has been easy for the Yankees across the first two months of the season, so why should it start now.

Now Pettitte, the horse of the staff, has a potential problem. And nobody really knows what the MRI exam Clemens is having today will find in the groin area.

Yet, there is no time for alibis. A-Rod is right: It’s time the Yankees started putting things together. Last night Rivera and A-Rod did exactly that.

george.king@nypost.com