"I suffered, that's the right word", said Nadal after playing his longest ever match at the tournament.
"I am playing a lot of hours on this attractive stadium, that does not bother me - it just bothers my legs", he said. Even like this, I had a very lucky first set.
"I just said "I am very sorry". He has plenty of time to win.
Rafael Nadal, who is ranked world number one, stormed his way into the semi-final of the ongoing US Open on Wednesday after overpowering Austria's Domenic Thiem in a fierce encounter played at the Arthur Ashe Stadium.
"When I get to a grand slam, I feel I want to play really hard".
Nadal stole a break to stay in the set, held quickly for 6-5 and cashed his third set point on the Thiem serve with a missile of a forehand victor.
Nadal, who was on court for four hours and 48 minutes in a tie which finished at 2.04am local time in NY (7.04am BST), commented on the humidity of the playing conditions that has troubled so many players in this year's Open, and broke down his performance.
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The disappointment of failing to create a first match point seemed to weigh on him in the tiebreak and he played it dreadfully, showing rare confusion in going 0-3 down and then losing it 7-4.
World number one Nadal lost the opening set 6-0 after being outpowered by the Austrian ninth seed in NY.
The Spaniard secured the break he wanted for 5-3 only to give it back but a sloppy game from Thiem, who turned 25 on Monday, handed him the set anyway.
What channel is Rafael Nadal vs Dominic Thiem on? The fourth was an 81-minute rollercoaster ride, where Nadal came within two points of winning only for Thiem to take the tie-break. But once again Nadal stepped up the level, saved two break points in the game and then went on to claw back to 4-4. ESPN captured that perfectly in a triumphant photo of the 32-year-old.
With the clock ticking towards 1am and transport options dwindling, many fans headed for the exits while the two adversaries battled on. "He's a fighter, he has a great attitude". Nadal said of Thiem.
That they were still able to produce tennis of such quality was astonishing.
The Spaniard saved a break point in games nine and 11 but he stood no chance in the tie break, losing it 7-4 following a routine forehand that he sent into the net, handing the set to his rival and setting up a decider after more than three and a half hours of unbelievable battle! But when he came out to serve for the set at 5-4, the Austrian was visibly hesitant, Nadal bounded behind the baseline. "Keep going", the victor said of the embrace.
There are no chill Rafael Nadal matches, like oh cool, I'll watch some tennis and my blood pressure will stay level.