New Delhi, Nov 18 (IANS): World No. 6 Stefanos Tsitsipas of Greece defeated tournament debutant Andrey Rublev 6-1, 4-6, 7-6(6) at London's O2 Arena to set up a virtual quarter-final clash with Rafael Nadal for a place in the semi-finals.

Tsitsipas's win over Rublev guaranteed Austria's world No. 3 Dominic Thiem a place in the semi-finals. Thiem now leads the Group London 2020 2-0.

"It was an unbelievable match from both sides. We produced some incredible tennis," Tsitsipas said after the match.

"The relief at the very end of putting all that effort and all that fight on the court paid off. I am very happy that I showed determination and a willingness to not give up when he had match point. It came easier when he was up 6-5, but then I produced some really good tennis and that helped me take the win," he added.

The Greek player had played a tough three-set match against Thiem on Sunday. The match against Rublev too went the distance. Rublev won four consecutive points from 2-5 down in the final set tie-break to earn match-point. The Russian double faulted, though, and Tsitsipas took full advantage.

"Having the opportunity to play lots of matches like this, at such a high intensity, and always testing myself against these players gives me the opportunity to learn and grow," Tsitsipas added.

"It is a learning opportunity as well for today. Even though it was a win, I still feel like there is plenty to improve and get better at. I am sure being with that mindset, being willing to just put more and more effort into what I am doing and more sacrifices are going to pay off at the end."