CHICAGO - Jose Contreras has certainly become the dominant pitcher the Yankees paid for. He just didn’t do it until he left New York.

“For me, nothing has changed. I just kind of worked more on my mental and physical health,” the Chicago ace said through a translator on Friday. “I have no pressure with the White Sox.”

Not long ago, Contreras, Roger Clemens, Andy Pettitte and Orlando Hernandez were all in the Yankees’ rotation.

Now they’re all in the World Series, ready to pitch without their pinstripes.

It must be enough to make George Steinbrenner cringe.

“It’s definitely strange,” Pettitte said as his Houston Astros prepared to face Chicago. “I know it’s special for me and Rog, and it’s definitely special for those guys, too.”

They left New York for different reasons: Contreras was a castoff, Clemens had retired, Pettitte became a free agent and El Duque rejected an arbitration offer.

But when Pettitte signed with Houston after the 2003 season, Clemens changed course and joined his buddy back home. Contreras and Hernandez eventually landed in Chicago, and all four flourished one way or another.

Each pitched in the World Series for the Yankees. Now they’ve all returned — before New York did so without all of them.

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“I don’t know that we’ve ever even worried about that,” Clemens said.

Not so sure that’s the case back in the Bronx.

For the Yankees and their fans, Contreras is probably the most difficult success story to swallow. He signed a $32 million, four-year contract with New York in February 2003 after defecting from Cuba, but quickly became a major bust.

Wildly inconsistent and lonely without his family, he never lived up to lofty expectations, partly because he was sidelined for 2½ months with a strained shoulder. Plus, Contreras struggled most against the rival Red Sox — and that’s a sure ticket out of town.

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Despite his so-so numbers overall, the White Sox always coveted the big right-hander with the nasty splitter. So the Yankees shipped him to Chicago at the 2004 trade deadline for two-time All-Star Esteban Loaiza in a deal that didn’t look half-bad at the time.

“I was mad because I had a lot of friends in New York,” Contreras said. “But I had to just step through that, go through it, and when I got here I wanted to thank the organization for just giving me the confidence.”

Turns out, the White Sox got a steal.

Teamed with a fellow Cuban in Hernandez (they spent only a few weeks together on New York’s roster last year) and comfortable in his new surroundings, Contreras blossomed in the second half this season, going 11-2 with a 2.96 ERA.

He stopped tipping his pitches and made some mechanical adjustments, dropping his arm angle at Hernandez’s suggestion. The results were more strikes, more innings and more outs.

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“I don’t know, nor do I really care, about what went on in New York with Jose,” Chicago pitching coach Don Cooper said. “I think Contreras’ future is ahead of him.”

Contreras became the team’s No. 1 starter down the stretch and went 2-1 with a 2.88 ERA in the AL playoffs to help the White Sox reach the World Series for the first time since 1959. Now, he’ll start Game 1 of the World Series on Saturday night against Clemens, who taught Contreras how to throw a four-seam fastball during their days in New York.

“We trust him and believe in him. He was so insecure,” manager Ozzie Guillen said. “The thing about Jose was, he don’t want to let people down. When he signed a big contract, people talked about how much money he made, he should win every game.”