New York:Juan Martin del Potro became the lowest ranked player in 25 years to reach the US Open quarter-finals Monday, setting up a showdown with fellow Grand Slam title winner, Stan Wawrinka.
The 142nd-ranked del Potro was leading eighth-seeded Dominic Thiem 6-3, 3-2 when the Austrian retired with a right knee injury.
Del Potro, the 2009 US Open nchampion who was pushed to the brink of retirement earlier this year after undergoing three surgeries on his left wrist, will next face third seed Wawrinka for a semi-final place.
Wawrinka, a former Australian and French Open champion, reached a fourth successive quarter-final in New York with a hard-fought 6-4, 6-1, 6-7 (5/7), 6-3 win over Illya Marchenko, the world number 63 from Ukraine.
"You never want to win a match like this. I wish Dominic a quick recovery as he has a great future," said 27-year-old del Potro, the lowest-ranked man in the last-eight since Jimmy Connors, at 174, went all the way to semi-finals in 1991.
The giant Argentine had required treatment himself on a right shoulder injury after dropping serve to go 2-1 down in the first set.
But he recovered to break back for 3-3 before edging ahead at 5-3 and taking the opener on an ace.
Del Potro was a break to the good again at 2-1 in the second set before Thiem began to flag.
The 23-year-old Austrian had needed five sets to beat Australia's John Millman in the first round and four to get past Pablo Carreno Busta of Spain in the last 32.
"I couldn't bend my knee too much in the last three days so I was handicapped a little bit," said Thiem.
He was also playing in a season-leading 70th match of the season and 21st tournament, a gruelling schedule which finally caught up with him on Arthur Ashe Stadium.
Should del Potro make the semi-finals he would be the lowest-ranked man to do so at a Grand Slam since 237th-ranked Vladimir Voltchkov at Wimbledon in 2000.
No man ranked as low as del Potro has ever made the final of a major.
Having saved a match point in an epic triumph over Dan Evans in the last round, Wawrinka, a semi-finalist in 2013 and 2015, cruised through the first two sets against Marchenko.
The Ukrainian, who arrived in New York on a seven-match losing streak, battled back from 2-4 and 3-5 down in the third set to force a tiebreaker.
He was a break to the good at 2-1 in the fourth before Wawrinka, reinvigorated by a violent racquet smash courtside, recovered to win five of the next six games.
"It was tough to lose that third set but I am looking at the big picture," said 31-year-old Wawrinka, whose 49 winners helped offset his 41 unforced errors.
"It'll be great to play Juan Martin again. It will be a great challenge."
Nishikori halts Karlovic
Japanese sixth seed Kei Nishikori spiked the big guns of 37-year-old Ivo Karlovic to book his last-eight spot.
The 2014 runner-up swept to a 6-3, 6-4, 7-6 (7/4) win and will face either second seed and 2012 champion Andy Murray or Grigor Dimitrov of Bulgaria for a place in the semi-finals.
Karlovic fired 21 aces in the contest but Nishikori's 44 winners and a miserly seven unforced errors proved the key.
Murray closes the night session on Monday protecting a 6-3 head-to-head lead over Dimitrov although the 25-year-old Bulgarian won their last match in Miami in March.
The first two quarter-finals take place on Tuesday when defending champion Novak Djokovic faces France's Jo-Wilfried Tsonga and Lucas Pouille, the conqueror of Rafael Nadal, tackles French compatriot Gael Monfils.