NEW YORK (AP) A Monday men's final is becoming a U.S. Open tradition.

The championship match between Rafael Nadal and Novak Djokovic was postponed a day because of persistent rain Sunday, the third consecutive year that the season's last major tournament won't finish on schedule.

The No. 1-seeded Nadal, bidding to complete a career Grand Slam, and No. 3 Djokovic were supposed to begin playing at 4:30 p.m. Sunday, but showers began more than 1 1/2 hours earlier and hadn't stopped by 6:15 p.m., when tournament officials decided to call it a night.

The final was rescheduled for 4 p.m. Monday, when the forecast calls for a 20 percent chance of thunderstorms.

Before 2008, the U.S. Open men's final hadn't been pushed to Monday since 1987. But Roger Federer beat Andy Murray on a Monday two years ago, then lost to Juan Martin del Potro on a Monday last year. This marks the first three-year string of delayed finishes at the tournament since the men's and women's singles competitions were combined and played at the same site in 1935.

It was a very uncertain forecast, and had been shifting over the course of the day. We are in a band of showers that potentially could stretch until 1 (a.m.),'' U.S. Tennis Association spokesman Chris Widmaier said.There may be breaks in there, but it was such an uncertain forecast that we felt the right thing to do for the players - and certainly for the fans - was to postpone the remaining matches until tomorrow.''

Nadal and Djokovic were told a little before 6:30 p.m. that they wouldn't be playing Sunday, Widmaier said.

At 3 p.m., Djokovic was warming up on a practice court right outside Arthur Ashe Stadium as scattered drops fell. A few dozen fans - some holding aloft umbrellas - gathered outside the fence, catching a glimpse of the 2008 Australian Open champion.

He probably doesn't mind having to wait until Monday to play for real. That's because he reached the final with a grueling, five-set victory over Federer that lasted about 1 1/2 hours more than Nadal's straightforward, three-set win against Mikhail Youzhny in Saturday's first semifinal.

The U.S. Open is the only Grand Slam tournament that schedules its men's singles semifinals and finals on back-to-back days, which could have proved to be a disadvantage for Djokovic. Indeed, after upsetting Federer on Saturday to reach his third Grand Slam final, Djokovic opened his eyes wide and rubbed his hands together when he was told about the possibility of rain affecting the final.

I don't know the rituals; how to invite the rain,'' he said.An extra day would be great.''

Well, now he got it.

Nadal, meanwhile, will have to wait at least a day for his shot at history. Playing in his first U.S. Open final, the Spaniard is seeking to become the seventh man to own at least one singles title for each of tennis' four more prestigious tournaments.

He takes a 20-match Grand Slam winning streak into Monday, having won the French Open and Wimbledon to raise his major title total to eight. A victory over Djokovic also would make the 24-year-old Nadal the first man since Rod Laver's true, calendar-year Grand Slam in 1969 to win at Paris, London and New York in the same season. And it would send Nadal to the Australian Open in January with a chance to pull off a Rafa Slam of four major titles in a row, something no man has done since Laver.

There was only one interruption of play because of rain during the first 13 days of the tournament, a delay of about 25 minutes on the first Friday, when the outer bands of Hurricane Earl passed through the area. Otherwise, Week 1 was all about the heat, with the temperature reaching into the mid-90s, and Week 2 was all about the wind, with gusts topping 30 mph.

While Djokovic was training Sunday afternoon, the women's doubles final was halted in progress, with Liezel Huber and Nadia Petrova three points from victory at 5-4 in the third set against Vania King and Yaroslava Shvedova. Tournament referee Brian Earley and tournament director Brian Curley went on the Arthur Ashe Stadium court to check the conditions, and eventually, the players were sent to the locker room.

About 45 minutes later, heavier rain began falling, and the doubles final was scheduled to resume Monday at 3 p.m. - weather permitting.

There were some matches completed before the rain set in Sunday, including the first all-American U.S. Open boys' final in a decade. Jack Sock, a 17-year-old high school senior who grew up in Lincoln, Neb., beat Denis Kudla 3-6, 6-2, 6-2 to become the first player representing the United States to win the title since Andy Roddick in 2000.

Top-seeded Daria Gavrilova beat Yulia Putintseva 6-3, 6-2 in an all-Russian girls' final, while Esther Vergeer won her 396th consecutive match by defeating Daniela di Toro 6-0, 6-0 in the women's wheelchair final.