RAFAEL NADAL began his U.S. Open quarterfinal as poorly as possible, shut out in a set by a 6-0 score for only the fourth time in 282 career Grand Slam matches.

On the previous three such occasions, he’d lost. On this one, he managed to come back to win, although it took 4 hours, 49 minutes and never did get easy for him.

The defending champion and No. 1 seed at Flushing Meadows recovered from his disastrous start and other stumbles along the way to beat No. 9 Dominic Thiem 0-6, 6-4, 7-5, 6-7 (4), 7-6 (5) for a semifinal berth at a third consecutive Grand Slam tournament, winning a physical, back-and-forth tussle that concluded after 2 a.m. yesterday.

How tense and tight was this one? Not only was Nadal two points from losing at 5-all in the closing tiebreaker, but he finished with fewer total points, 171-166.

“It’s cruel, sometimes, tennis,” Thiem said, calling the loss “the first really epic match I’ve played.”

When it ended, on an overhead by Thiem that sailed long, everyone in Nadal’s guest box — a group that included actor Ben Stiller — leaped to their feet to celebrate. Nadal climbed over the net to hug his opponent , then whisper an apology and words of encouragement.

“I’m very sorry for Dominic,” Nadal told a rowdy crowd in Arthur Ashe Stadium. “He’s a close friend on tour. He’s a great guy. A great player.”

Asked about that at his news conference, Thiem said with a chuckle: “Well, I don’t think he’s really sorry.”

This rematch of the French Open final in June, won by Nadal, was his first match against a top-20 opponent at the U.S. Open since 2013, when he beat then-No. 1 Novak Djokovic in the final.

It sure seemed at the shocking outset as if Nadal was somehow unprepared for this step up in competition. Thiem collected 24 of the opening set’s 31 points, thanks in large part to a 13-3 edge in winners.

Hard to not think back to 24 hours earlier, when Nadal’s great rival, No. 2 seed Roger Federer, was upset in the fourth round during similarly muggy conditions. Nadal was sweating so much in the heat and 50-percent humidity that a mountain of white towels formed next to his changeover bench.

The depth and strength of Thiem’s groundstrokes were doing what Nadal’s shots usually do to opponents: robbing them of time and space. Plus, Thiem — an Austrian who turned 25 Monday — was serving well, taking every point when he put a first serve in, and handling returns without a hitch.

It took a while for Nadal to figure out what was wrong and become Thiem’s equal in entertaining, body-punishing baseline exchanges that inspired loud gasps from spectators. Still, this whole contest was filled with challenges for Nadal. He fell behind by a break in the third set before rebounding. He was two points from victory at 6-5, deuce, in the fourth as Thiem served, but flubbed a forehand volley, leaping for a ball that appeared to be sailing out and dumping it into the net.   (SD-Agencies)