(Reuters) - Belarusian Daniil Ostapenkov, a junior player who has not played professional-level match before, stunned world number 15 Diego Schwartzman 6-4 6-3 in their World Group I Davis Cup match on Saturday.
The 18-year-old became the latest young gun to cause an upset following a U.S. Open where teenagers seized the spotlight and 18-year-old Briton Emma Raducanu became the first qualifier to win a Grand Slam title.
Ostapenkov fired down three aces and saved seven break points to defeat Argentina's Schwartzman on his home turf at the Buenos Aires Lawn Tennis Club.
The win gave Belarus a 1-0 lead in the best-of-five match against the 2016 champions.
The teams playing in World Group I are bidding for a place in the 2022 Davis Cup qualifiers, a step closer to the Finals.
(Reporting by Amy Tennery in New York; Editing by Toby Davis)