Dominic Thiem inflicted Rafael Nadal's first defeat on clay since the Austrian's victory over him in Rome previous year to reach the semi-finals of the Madrid Open, meaning Roger Federer will return to world number one.
"Of course I am disappointed", Nadal said.
Nadal and Thiem have met eight times so far in their careers, and interestingly all eight meetings have come on clay courts.
Monfils brought it up during an interview after the match Wednesday and seemed rattled despite Nadal's serve timing not contributing too much to the end result, which was a dominating win for the Spaniard.
'Talking about No. 1, of course I prefer to be No. 1 than 2, and No. 3 than 5.
"Last year was little bit different", said Thiem about the match up. I lost the No. 1 before, but what makes me happy is I feel fit, can compete with possibilities every single week. "And waiting for some shorter ball and then I'll attack", said the 26-year-old. However, he upset the Spaniard in Rome a year ago, winning 6-3 6-3. I didn't play badly in my opinion. "It was one of those golden matches".
I give the Thiem the edge, but likely in three sets. "It takes the same". It was an overall impressive performance from Thiem, who has now beaten Nadal three times on clay.
"Very tough match. Especially here on this surface and even more in altitude".
Nadal, who received a bye in the opening round, fired 17 winners and went on to lose just one of 13 service points in the second set to seal victory. "I need to be ready for tomorrow. The feelings are very good", he had said.
World number six Juan Martin del Potro crashed out of the tournament after Serbia's Dusan Lajovic came back from a set down to beat the Argentine 3-6 6-4 7-6 (6) in the third round.
"It's for sure my best win, and definitely one of the best matches I've played". It was a match the Croatian will feel he should have won having served for it up 6-2 5-4. "This is my second week on clay and I found it hard from a physical stand-point".
Lajovic will now face Kevin Anderson.
In the only match of the day without a seeded player, Canadian Denis Shapovalov defeated countryman Milos Raonic 6-4, 6-4.