Cablevision’s 3.1 million subscribers in the tri-state area were unable to watch one of the biggest upsets in U.S. Open history — the Andy Roddick-John Isner five-set war that ended in a 7-5 tiebreaker at 9:15 last night.

CBS dropped out of its day coverage at 5:58 p.m. during the first set, with the score 4-3 Isner. The Tennis Channel, for the first time, picked up the exclusive coverage after 6 p.m., carried Roddick’s comeback from two sets down before he fell in the fifth. Cablevision does not carry Tennis Channel because of a contract dispute.

“We’re getting rave reviews except from poor Cablevision subscribers,” Tennis Channel CEO Ken Solomon told The Post. “Maybe this will change their mind.” Cablevision fans could watch the match only on the Internet via the Open’s Web site. Cablevision’s stance is it technically has an agreement to show Tennis Channel and the network is holding out. Customers of Time Warner had access to the match, but on a higher-priced sports tier.

The Tennis Channel was available in 55 million homes nationwide last night.