He failed to hold on to an early break for 3-1 as the 49th-ranked Tiafoe broke back right away, but Zverev broke the 49th-ranked American again at 6-5 when Tiafoe hit a forehand wide.
Tiafoe held off four break points in the second set before he missed his only chance on Zverev’s serve at 4-4.
Tiafoe lost his next service game without scoring a point as Zverev closed out the win with a backhand return.
“Frances is a very dangerous opponent, especially when he’s having fun on the court,” Zverev said. “If he keeps it up, he might be top 10 next season. The tennis he has shown this week was really world class.”
Tiafoe impressed at the Austrian indoor event with two come-from-behind wins. He beat top-seeded Stefanos Tsitsipas after battling back from trailing 3-0 in the final set, and ended an 11-match winning run from Jannik Sinner as he recovered from a set and 5-2 down against the Italian.
It was the first tournament for Tiafoe with more than one win against a top-20 opponent.
“This is the best week I’ve had in my career. It’s really emotional for me,” Tiafoe said. “I can’t wait for what is going to happen in 2022, hopefully some great things.”
Zverev improved to 6-1 in career meetings against Tiafoe, who only beat the German at the Cincinnati Masters in 2017.