The final lasted four hours, but at first looked like it could be a walking victory for the German Alexander Zverev, who convincingly took home the two initial sets.
In the third, Thiem managed to come back and the final developed into a thriller in five sets that went to a decisive tiebreak.
In the end, Thiem was able to see Zverev hit a return off the field and the Austrian lay exhausted on his back behind the baseline and cheered on the victory with 2-6, 4-6, 6-4, 6-3, 7-6 and 8-6 in the tiebreak .
"Friendship and rivalry"
-We started getting to know each other in 2014 and immediately developed a nice friendship, and in 2016 we started a fantastic rivalry.
We have done fantastic things both on and off the pitch.
I wish we could have had two winners today.
We both deserve it, says Thiem in his victory speech.
The final between two players who have never won a grand slam title before was marked by nervousness and a lot of simple mistakes.
Thiem was also marked by cramps during the fifth set and limped precariously between the balls in the tiebreak.
First time since 1949
Never before since the US Open in 1968 was opened for professional players has a finalist managed to bring home a 0-2 deficit and win a final.
In fact, the last time this happened was in 1949 when the competition was called the US Championships.
It was also the first time that a final was decided in tiebreak in the fifth set and 27-year-old Thiem is the US Open's first champion on the men's side who was born in the 1990s.
It is also Thiem's first grand slam title, he has reached the final of the Australian Open earlier this year and in the French championships both 2018 and 2019.