Forget about that regular season for a second because it’s not about that anymore. This is the playoffs. This is Yankees-Red Sox. And this is all that matters.

And that’s why what Gary Sheffield is doing is so impressive.

“He doesn’t crack under pressure,” none other than Reggie Jackson said of Sheffield late last night. “He rises up to it.”

In his first October as a Yankee, Sheffield is simply having a splendid postseason, and an even more dominant ALCS. He didn’t waste any time delivering again in last night’s 3-1 Yankee win. In the first inning, with two on, none out and Pedro Martinez on the mound, Sheffield stepped up, cocked his bat furiously and took a ferocious cut at Martinez’s first pitch.

Then he slashed it into centerfield for an RBI single and a 1-0 Yankee lead.

The fans immediately broke into their “M-V-P!” chant for Sheffield. But while that’s certainly high praise, the MVP award is handed out for regular-season performance.

Sheffield, however, is getting the job done in October. And in particular, he’s getting the job done in his first playoff encounter with the Red Sox.

“This is what everybody wanted to see,” Sheffield said of Sox-Yanks, “and we’re giving them a good show right now.”

Sheffield is a big reason why. In his first postseason go-around with the Yankees, Sheffield has picked up right where his superb regular season left off. He’s hitting .346 (9-for-26) with a homer, three RBIs and a team-high six runs scored in six games.

In the ALCS alone Sheffield is hitting an absurd .625 (5-for-8).

Just as important as his production, though, Sheffield has shown how much he understands the eye-bulging intensity and white-hot spotlight that comes with Yankee-Red Sox playoff baseball.

Heck, he showed it in Game 1 of this series when he ripped three hits and scored four runs. The second run he scored came in the third inning when he raced around the bases and scored from first on Hideki Matsui’s bases-loaded double.

After sliding in safely, Sheffield popped up and chest-bumped A-Rod so hard, Sheffield’s helmet flew off. At that point, it became pretty clear – yep, Gary Sheffield gets Yankees-Red Sox.

“I’ve never seen him so excited,” Jackson said.

Sheffield came through again last night. New opponent. New time of year. Same clutch player.