New York - Dominic Thiem admitted he's "not sure" if he can defeat defending champion Rafael Nadal at the US Open and reach the semi-finals.
The 24-year-old Austrian faces the world number one on Tuesday, just three months after he was routed by Nadal in the final at Roland Garros.
That loss was one of seven he has endured at the hands of Nadal in his career.
He does has the comfort of knowing that he has been successful on three occasions.
However, like Nadal's wins against him, the Austrian's three successes have all come on clay, easily his most comfortable surface.
"I have had three very nice experiences and seven horrible experiences," said Thiem, who has made the last-eight at a Slam other than Roland Garros for the first time.
"But I'm really looking forward to play him on a hard court for the first time.
"On clay, I think it's one of the biggest challenges in sports to beat this guy or to compete with this guy.
"I hope that it's a little bit more comfortable on hard court, but I'm not sure."
Thiem at least knows that even if all three of his wins against Nadal have been on clay, they were still key moments.
His victory against the world number one in the Madrid semi-finals ended Nadal's 50-set clay win streak which began after the Austrian had beaten him in Rome 12 months earlier.
Thiem also remains the only member of the top 10 that Nadal has never tackled on a hard-court.
"Nobody's game really matches up well with his," added Thiem who made his first US Open quarter-final with an impressive 7-5, 6-2, 7-6 (7/2) win over last year's runner-up Kevin Anderson, the fifth-seeded South African.
"That's why Rafa is so unbelievably successful. No matter what, it's always really tough to play against him."
Thiem didn't face a single break point against Wimbledon finalist Anderson as he became the first Austrian in the last-eight in New York since Thomas Muster in 1996.
Nadal, the 2010, 2013 and 2017 champion and chasing an 18th major, believes the change from clay to hard court will not alter the dynamic on Tuesday when he plays his eighth quarter-final at the tournament.
"It's a different kind of match than clay, but is still a tennis match," said Nadal.
"Dominic is a fantastic player. He's a very powerful player. He deserves to be where he is."
US Open results on Sunday, the seventh day of the 2018 tournament at Flushing Meadows (x denotes seeded player):
Rafael Nadal (ESP x1) bt Nikoloz Basilashvili (GEO) 6-3, 6-3, 6-7 (6/8), 6-4
Dominic Thiem (AUT x9) bt Kevin Anderson (RSA x5) 7-5, 6-2, 7-6 (7/2)
Juan Martin Del Potro (ARG x3) bt Borna Coric (CRO x20) 6-4, 6-3, 6-1
John Isner (USA x11) bt Milos Raonic (CAN x25) 3-6, 6-3, 6-4, 3-6, 6-2
Serena Williams (USA x17) bt Kaia Kanepi (EST) 6-0, 4-6, 6-3
Karolina Pliskova (CZE x8) bt Ashleigh Barty (AUS x18) 6-4, 6-4
Sloane Stephens (USA x3) bt Elise Mertens (BEL x15) 6-3, 6-3
Anastasija Sevastova (LAT x19) bt Elina Svitolina (UKR x7) 6-3, 1-6, 6-0