Before Saturday, 29-year-old Thiago Monteiro had never advanced beyond the second round of an ATP Masters 1000 event.

Taking inspiration from the likes of Adrian Mannarino and Jan-Lennard Struff, the Brazilian channeled his “it’s never too late” mantra to unlock the new milestone, beating one of the hottest competitors in the process.

Monteiro put on an impeccable serving display to oust No. 6 seed Stefanos Tsitsipas, 6-4, 6-4. The 118th-ranked qualifier did not face a break point until he served for the encounter after missing a pair of match points against the Greek’s serve in the previous game. Monteiro, who made 89 percent of his first serves, would erase it before closing out Tsitsipas with an inside-out forehand winner.

“Here in the conditions, the serve, especially the left serve, works really well. The ball was bouncing high,” Monteiro told press.

“I knew I had a big challenge ahead against a top player, but I was feeling good.”

The left-hander celebrated his first completed Top 10 victory since defeating Holger Rune in a Davis Cup rubber in September 2023. Monteiro is a former world No. 61 and can get back inside the Top 100 if he advances past No. 30 seed Jiri Lehecka in the third round.

“Never too late indeed. I see guys like Struff that is (34), won his first ATP (title) last week. Mannarino, 35, he had his best season of his tennis career last year,” he said.

“Tennis is like this. One week can change the whole year, the whole plans that you have. You just need to keep working hard and to keep trying to enjoy it, take this opportunity when it appears.”

Tsitsipas has now dropped consecutive matches after opening his European clay-court swing with 10 successive victories. The former Roland Garros runner-up captured his third Monte Carlo crown before Casper Ruud avenged that final-round defeat by turning the tables in last Sunday’s Barcelona title match.

“I had a very good opponent on the other side of the net. He was coming up with great shots and punishing me every single time I played short. Didn’t manage to get the depth of the court,” assessed Tsitsipas.