Tsitsipas edged Griekspoor 6-7 (5), 7-6 (6), 7-5 after 2 hours and 59 minutes of playing time at Rotterdam's Centre Court. The Greek number 12 of the world admitted the game was "extremely close".
"It’s difficult to pick a winner in a match like this," Tsitsipas told reporters after the match. "Because both deserve a victory after trying for so hard for so long to win this match. He was extremely close and I came up with an amazing winner down the line to break him to and go up 6-5."
After beating qualifier Harold Mayot last Monday, Tsitsipas had two more days of rest than his Dutch opponent. But even with the additional rest, the Greek had to play a different tactic. "A little bit more daring, I'd say.
"I really went for it and I felt like that was a shot that was necessary at that point He was mixing it up, trying all kinds of variations and different things So I really had to do something more."
Tsitsipas and Griekspoor had met once before - the Greek won a meeting at the 2023 Australian Open, eliminating the Dutchman in straight sets in the second round of the Grand Slam.
"He (Griekspoor) seems more confident," Tsitsipas said. "But he was a little more daring and definitely much more stable."
Bellucci
Tsitsipas will meet qualifier Mattia Bellucci in the quarter-finals of the Rotterdam tournament - a player the Greek said he was "surprised" to see in the qualifiers for the tournament.
"I've been seeing him around on the tour and I think he is someone that plays good tennis. I was actually surprised to see him in quality because he's better tennis wise than qualifiers.
"I have to adjust enough to his game style. I have some experience playing lefties in the past, and some of them have a certain way they play think. The leftists have a certain approach against right-handed players."
The tall Greek will meet Bellucci during Friday's afternoon session. Whether or not he'll do that on the back of one of his best matches in recent memory? "It's up there, for sure."