Paraguayan qualifier Adolfo Daniel Vallejo said he felt like he was living "a movie" after he dispatched former world number three Grigor Dimitrov 6-4, 6-4 in the first round of the Madrid Open on Thursday.
The 21-year-old cracked the top 100 for the first time last month – following a 14-1 start to the season at the Challenger level – and is making his Masters 1000 debut this week.
He is the first Paraguayan to compete in Madrid Open history and will next take on American 17th seed Learner Tien.
"For me this is unbelievable. It looks like a movie, I don't know what's happening," Vallejo told Tennis TV.
"The other day I played on Manolo Santana centre court. Today I played here. I used to watch him (Dimitrov), all the highlights. The points that he did against me today, I used to watch it on TV and to play against him... wow, I can't understand what's happening. I'm just trying to enjoy all this."
Former world number three and 2019 Madrid runner-up Stefanos Tsitsipas eked out a 3-6, 7-6 (8/6), 7-6 (7/4) win against American lucky loser Patrick Kypson.
Currently ranked 80 in the world, the two-time Grand Slam finalist will square off with eighth-seeded Alexander Bublik in round two.
The soon-to-be-retiring Gael Monfils lost his opener 6-3, 6-4 to Camilo Ugo Carabelli, marking his last time competing at the Madrid Open.