Tsitsipas lost the chance to win the world No. 1 title after an epic showdown at Louis Armstrong Stadium, where world No. 94 Galán claimed victory on his ninth match point.
Picking up just seven points in the first set, Tsitsipas lost the first 11 games against the Colombian before coming back to his game and winning the third set.
“I think he started to play better in the third set. He served much better than the first two and I was putting the serve on the court but not putting pressure on him. He was still in control,” Galan said.
“I think he felt really comfortable during those two sets. I tried to change the position a bit when I was coming back and it changed a lot because I was able to come back. [deeper] and he wasn’t so attacking on the first ball, so I was able to do a bit more.”
Although Tsitsipas fought hard in the fourth, he was unable to hold off the Colombian, with Galán winning the set and the match.
“He dominated the game,” Tsitsipas said after the event. “I just couldn’t get into it.”
Meanwhile, Galán said his US Open main draw debut was “definitely the best match of my career, not only because of the circumstances, but also the opponent. I’m really happy.”
Galán will next face Australian Jordan Thompson.