The world number 63’s breakout week continued with a 6-3 6-2 dismantling of the Austrian third seed, supposedly an outsider for glory at next month’s French Open.
Tsitsipas, 19, had already beaten seeded Albert Ramos and Diego Schwartzman.
Nadal destroys Tsitsipas to take title and stretch clay winning streak
Elsewhere, second seed Grigor Dimitrov fell to Spain’s Pablo Carreno Busta 6-3 7-6(4).
World number one Rafael Nadal extended his winning run on clay to an incredible 42 consecutive sets as he beat Martin Klizan 6-0, 7-5.
Nadal looked like he would breeze past Novak Djokovic's conquerer when he bageled the first set.
But world number 140 Klizan made him sweat, getting three set points to potentially take it to a decider.
However Nadal dug deep and battled back to take the second game and charge into the semi-final.
He will face David Goffin in the semi-finals after he beat Roberto Bautista-Agut 6-7, 6-2, 6-2.
Nadal blasts past Goffin for 400th win on clay
Teenager Tsitsipas stages another upset to reach Barcelona final