But in the quarter-final, the second seed was less magnanimous than the mercurial Bulgarian. The Spaniard slapped down the youngster 6-3, 6-4, 6-2 in one hour and 47 minutes.
"I feel lucky to be where I am after what I went through to be able to compete at this level," said Nadal. "That's why I get up in the morning and go to the gym and work hard."
Nadal had never faced the American before. He broke him immediately and claimed the opener in 31 minutes.
"I knew he was going to bring crazy intensity," said Tiafoe. "I knew the ball was going to be jumping. Point in, point out, I've never seen someone so locked in."
Nadal will take on 14th seed Stefanos Tsitsipas from Greece in Thursday's semi-final after the 20-year-old disposed of the 22nd seed Roberto Bautista Agut in four sets.
"For me is always the same: you are in the semi-finals of a Grand Slam and you can't expect an easy opponent," he said of his next adversary.
"Stefanos is one of the best players of the world. To have the chance to be in thet final, I need to play my best and that's what I am looking for."