And Thiem, the only man to beat Nadal on clay for the last two seasons, set about showing his opponent he meant serious business in his first grand slam quarter-final outside of the French Open. But the last time, against Philipp Kohlschreiber in Miami last spring, he fought back to win the match.
That's just what the 17-time Grand Slam champion did over the course of a 4-hour 49-minute epic that concluded at 2:04 a.m. on Wednesday, September 5.
Thiem - with his girlfriend and fellow tennis player Kristina Mladenovic watching from the stands where Hollywood star Ben Stiller was also present - played well, however, Nadal was just too good as he executed the third of three set points on his opponent's serve to claim the momentum. The world No 1 and three-time victor at Flushing Meadows came within two points of victory, but Thiem wound up taking the fourth set on a tiebreak.
"The way it ended up in the fifth set tiebreaker, from there it's 50-50".
Leading 6-5 with a chance to take match point, Nadal mishit what looked like an easy volley into the net. "Have been physically demanding because the conditions have been tough out there", he said. "I don't know if I can get a new one, but I'm doing all my best to try to get it again".
Asked about that at his news conference, Thiem said with a chuckle: "Well, I don't think he's really sorry". "Forever I'm going to remember this match".
"He's young, he has plenty of time to win big tournaments. I'm playing a lot of hours this year at this handsome stadium".
When the ninth-seeded Thiem forced deuce in that game, Nadal rewarded his friend with a small clap from the other end of the court.
He fell behind by a break in the third set before rebounding.
"It's going to be stuck in my mind forever", Thiem said. That's one more today.
The semi-final will pit Nadal against third seed Juan Martin del Potro for the second successive Grand Slam.
The 4:48 match was the longest of Thiem's career-the 25-year-old had never played a match longer than four hours-and the longest one Nadal has played at the U.S. Open.
"To play John in these kind of matches, it's like an epic". I like to see that trophy every single day.
These two have faced one another 10 total includes including three times this year, though no previous meetings were during the US Open.
Despite that, the 29-year-old was never broken in the 3 hour 31 minute match where Isner unleashed 26 aces but was undone by 52 unforced errors compared to Del Potro's 14.