But in a titanic battle worthy of a final, with stunning winners on both racquets and breathtaking defence, top seed Nadal rallied to outlast Thiem 0-6 6-4 7-5 6-7 (4-7) 7-6 (7-5) in the longest match of this year's tournament - four hours and 49 minutes.
In 1992, Ivan Lendl defeated Boris Becker 6-7 (7-4), 6-2, 6-7 (7-4), 6-3, 6-4 in the fourth round that was described in media reports as the longest at the U.S. Open at the time, breaking the previous mark of 4 hours 54 minutes in the 1988 final between Lendl and Mats Wilander, won by Wilander 6-4, 4-6, 6-3, 5-7,6-4.
In an interview after his titanic battle, the 32-year-old Nadal gave credit to his opponent saying the match was very demanding in all aspects after almost five hours on court.
Nadal after worst start with the loss of 6-0 bounced back to beat No. 9 Dominic Thiem with 0-6, 6-4, 7-5, 6-7 (4), 7-6 (5) at a third consecutive Grand Slam tournament. "After that first set, then the match became more normal", said Nadal. Then, down 3-1, she faced three break points; if Pliskova won any, she would have led 4-1. Of course, my level dropped a little bit.
When it was finally over after 2 a.m. ET on Wednesday morning, Nadal and Thiem, clearly exhausted, walked over to each other for a hug, some words and a touching moment of class and sportsmanship at the net. "The only thing that I was thinking was to finish this first set and forget about this start". The way it ended up in the fifth set tiebreaker, there it's 50/50. "Tough match against a great opponent".
Asked about that at his news conference, Thiem said with a chuckle: "Well, I don't think he's really sorry".
The popular third seed will now attempt to take a step he has not managed since winning his only grand slam title here nine years ago and reach another final. He always plays and practices with a great attitude.
"I don't think he's really sorry", said the 25-year-old. But when he came out to serve for the set at 5-4, the Austrian was visibly hesitant, Nadal bounded behind the baseline.
"I'm happy that I did this for the first time, even if it went the wrong way".
"It's been a great battle, the conditions were tough, a lot of humidity".
Thiem made his intentions clear after clinching the opening set 6-0 as he made the Spaniard sweat hard to earn points in the quarter-finals clash. "It's good to have now two days (without a match) that probably give me the chance to be 100 percent in the semi-finals".
"We fought the whole match and I survived with my serve which was key".
"I had a shower, lay on the table and I didn't want to come back again".
Isner paid tribute to Del Potro.