New York - Stan Wawrinka reached the US Open quarter-finals for a fourth successive year on Monday with a 6-4, 6-1, 6-7 (5/7), 6-3 win over Ukraine journeyman Illya Marchenko.
Third seed Wawrinka, a semi-finalist in 2013 and 2015, will take on 2009 champion Juan Martin del Potro for a place in the last-four.
Del Potro, at 142 in the world, is the lowest ranked man in 25 years to reach the last eight.
The Argentine progressed when Austrian eighth seed Dominic Thiem retired from their last-16 tie with a knee injury. Del Potro was leading 6-3, 3-2 when Thiem quit.
Wawrinka had to save a match point in his epic third round win over Dan Evans and has yet to face an opponent ranked inside the top 45.
Results from the eighth day of the 2016 US Open tennis championships at Flushing Meadows on Monday (x denotes seeded player):
Juan Martin Del Potro (ARG) bt Dominic Thiem (AUT x8) 6-3, 3-2 - retired
Stan Wawrinka (SUI x3) bt Illya Marchenko (UKR) 6-4, 6-1, 6-7 (5/7), 6-3
Kei Nishikori (JPN x6) bt Ivo Karlovic (CRO x21) 6-3, 6-4, 7-6 (7/4)
Andy Murray (GBR x2) bt Grigor Dimitrov (BUL x22) 6-1, 6-2, 6-2
Serena Williams (USA x1) bt Yaroslava Shvedova (KAZ) 6-2, 6-3
Simona Halep (ROM x5) bt Carla Suarez Navarro (ESP x11) 6-2, 7-5
Ana Konjuh (CRO) bt Agnieszka Radwanska (POL x4) 6-4, 6-4
Karolina Pliskova (CZE x10) bt Venus Williams (USA x6) 4-6, 6-4, 7-6 (7/3)