The world number 27, who beat Dominic Thiem and Wimbledon champion Novak Djokovic on his way to the last eight, pulled off another upset with a 3-6, 7-6, 6-4 victory over the German at the Aviva Centre.

Tsitsipas, who will face Wimbledon runner-up Kevin Anderson in the semi-finals, became the first 19-year-old to beat three top 10 players in the same event since Rafael Nadal achieved the feat at the Monte Carlo Masters in 2006.

"I have no idea how I pulled off such an incredible comeback," the Greek player told Sky Sports. 

"It was an amazing effort I gave and I felt alive in every single point. 

"It was something I can probably say I can never really understand how all of this happened."

South African Anderson, who lost the Wimbledon final to Djokovic last month, booked his place in the last four by comfortably defeating fifth seed Grigor Dimitrov of Bulgaria 6-2, 6-2.

The other semi-final clash in the men's draw will be between 17-time Grand Slam champion Rafael Nadal of Spain and Russia's Karen Khachanov.

Top seed Nadal fought back from a set down to beat sixth seeded Croatian Marin Cilic 2-6, 6-4, 6-4, while Khachanov dispatched Dutchman Robin Haase 6-3, 6-1.

In the women's draw, Romanian top seed Simona Halep proved too strong for French opponent Caroline Garcia as she recorded a 7-5, 6-1 victory to set up a semi-final meeting with Australian Ashleigh Barty.

Barty was impressive in a 6-3, 6-1 win over Dutch player Kiki Bertens.

Third seed Sloane Stephens, last year's US Open champion, is also through after the American overcame Latvia's Anastasija Sevastova 6-2, 6-2.

The hard court competition is a World Tour Masters 1000 event for the men and a Women's Tennis Association Premier 5 tournament.