Tiafoe finished second in the fourth round of the US Open.
And defeated 23-time Grand Slam winner Rafael Nadal in four sets to achieve the biggest victory of his career.
He will face Andre Rublev in the last eight on Wednesday.
Tiafoe thrilled the home crowd with a 6-4, 4-6, 6-4, 6-3 win over four-time champion Nadal in New York.
Nadal is not sure when he will play again after the loss.
Tiafoe had never won a set against Nadal.
Tiafoe, 24, says he is more experienced now, and won't be afraid to go up against his legendary rival.
Tiafoe hasn't lost a set in the fourth round so far.