Rafael Nadal celebrates after his match against Diego Schwartzman of Argentina at the 2019 US Open. Photo: Geoff Burke-USA TODAY Sports

NEW YORK – Diego Schwartzman may have been the smallest player in 25 years to reach the U.S. Open quarter-finals but gave Rafa Nadal a big fight and forced the Spaniard to grind out a 6-4 7-5 6-2 win on Wednesday to reach the last four at Flushing Meadows.

With Roger Federer and 2018 champion Novak Djokovic having already made exits, Nadal's path to a fourth U.S. Open trophy has been cleared of familiar hurdles.

But Schwartzman reminded Nadal that danger can lurk everywhere, even from an opponent he had beaten in all seven previous meetings and only lost two sets.

Schwartzman, who often trains with Nadal, had the second seed's full respect after brushing past sixth seed Alexander Zverev in the previous round.

That caution was well placed as Schwartzman made the 18-time Grand Slam winner work for every point, with the Argentine fighting back from two breaks down in the opening two sets.

Subscribe to the IOL Sport Newsletter!

Nadal had come out firing on all cylinders showing the 5'7" (1.70m) tall Argentine no mercy as he raced to a 4-0 lead.

But Schwartzman dug in and threw everything he had back at the three time U.S. Open champion to send a shock through Arthur Ashe Stadium when he swept the next four games to level the set.

Rafael Nadal hugs Diego Schwartzman of Argentina (L) after their quarterfinal match at the 2019 US Open. Photo: Geoff Burke-USA TODAY Sports

The Spaniard, who has also never shied away from a fight, held serve and then broke his opponent for a 1-0 lead.

Normal service looked to have resumed in the second set as Nadal, bathed sweat, constructed a 5-1 advantage but again the 20th seed refused to surrender and stormed through the next four games.

The 33-year-old Spaniard, however, again broke Schwartzman for a 2-0 advantage.

Neither player was able to gain an edge in the third set until Nadal broke to go up 4-2, then delivered the knockout punch as he held serve and closed out the match with another break.

He now faces big-hitting Italian Matteo Berrettini, who ground out a 3-6 6-3 6-2 3-6 7-6 (5) over France's Gael Monfils, in the semi-finals.

Reuters