More than half a century ago, the prospect of two New York City teams grappling over a World Series championship was almost an expectation. But as baseball expanded west -- and took two New York teams with it in the process -- the odds of a true, old-fashioned Subway Series became more remote. That’s what made the 2000 World Series between the Mets and Yankees so memorable, and on what is (believe it or not) the 20th anniversary of that Fall Classic, many of that series’ biggest figures have come back together to relive an October week that is still remembered on both sides of the East River as if it were played yesterday.

Major League Baseball and FOX Sports Films have partnered for a special documentary, “When New York Was Won,” that dives deeper into the 2000 Subway Series than any piece of media before. Premiering Thursday night on FS1 immediately following the National League Championship Series Game 4 postgame show, the documentary gives a specific look at the interborough rivalry between the Mets and Yankees but also provides a larger view at how rivalries bring fans from different walks of life together.

Written and directed by Aaron Cohen, the documentary includes archival clips and interviews with stars from both clubs, including managers Joe Torre and Bobby Valentine, and former players including Andy Pettitte, Bernie Williams, David Cone, Al Leiter and Edgardo Alfonzo.

“Every morning talk show that normally talks about music and cooking and fashion was Yankees and Mets,” Leiter recalls of that week in America’s biggest city.

Adds Torre: “You really couldn’t escape it. From the time you woke up in the morning until the time you went to sleep, it was all about ‘New York-itis.’”

But the documentary’s biggest headliners are former Yankees ace Roger Clemens and former Mets catcher Mike Piazza, whose confrontations including the broken-bat incident in Game 2 defined the 2000 World Series. Clemens and Piazza both sat down for interviews for “When New York Was Won,” providing never-before-heard insights on their famous showdown.

Though the Yankees defeated the Mets in five games, capturing their third World Series championship in a four-year span, it was a nail-biter series with each contest decided by two runs or fewer. It was a momentous battle that the men on both sides will never forget.

“That whole city stood still and was watching those games,” Piazza says of the Subway Series, which wrapped up less than a year before the terrorist attacks of Sept. 11, 2001, changed New York forever. “History has taught us that when things are going well, enjoy them, because they can change in an instant.”