The feds’ key witness in the NYPD corruption scandal was living it up at the World Series — where a TV camera caught him rooting for the Cleveland Indians in a prime seat behind home plate at Wrigley Field on Sunday night.

Crooked real estate developer Jona Rechnitz was wearing an Indians cap and was linked arm-in-arm with a fellow Cleveland fan as they hoped in vain for victory against the Chicago Cubs.

Rechnitz pleaded guilty to bribing high-ranking cops and the former head of the correction officers union and agreed to testify against them. His good fortune left some cops fuming.

“All the cops involved got arrested or forced to retire and this guy’s sitting in a $3,000 seat. Where’s the justice?” said one law enforcement official.

Rechnitz’s lawyer didn’t respond to inquires. A spokeswoman for Manhattan US Attorney Preet Bharara declined to comment.