American Jack Sock knocked former champion Marin Cilic out of the US Open while world No.1 Novak Djokovic was given another rapid advance when Russian Mikhail Youzhny retired with injury.
Sock scored a power-packed 6-4 6-3 6-3 third-round victory at Flushing Meadows and in the last 16 he'll face ninth-seeded Frenchman Jo-Wilfried Tsonga, a straight sets winner against South African 23rd seed Kevin Anderson.
Sock, who battled back from a two-set deficit to beat the Croat in a Davis Cup duel in July, was impeccable on serve as he did not face a single break point while converting four of six break opportunities against the seventh-seeded Cilic.
"My first time in the fourth round here," Sock said in an on-court interview after dismissing the 2014 US Open winner. "It was a big match for me, a big goal of mine."
With the win, the 26th-seeded Sock matched his previous best grand slam advance, having reached the fourth round at last year's French Open.
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"There's nothing better than playing in front of the home crowd here in New York," Sock said. "I put it out there on the line on every point."
Top seed Djokovic cannot seem able to get an on-court workout after Youzhny retired due to a leg injury when trailing 4-2.
Youzhny was treated during the changeover at 4-1 in the third-round match at Arthur Ashe Stadium and had his left thigh taped. He won the next game on his serve but could not continue, giving Djokovic a pass into the round of 16.
The Serb, winner of this year's Australian Open and French Open to complete a career grand slam, came into the match off a three-day break due to a walkover into the third round when Jiri Vesely of the Czech Republic withdrew.
"It's difficult to pick the words now. I don't think I ever had this kind of situation in my career, where I had a second-round walkover and the third round 30 minutes only," Djokovic said on court before heading off to practice.
Defending champion Djokovic will next face 21-year-old Briton Kyle Edmund, who upset 20th-seeded American John Isner 6-4 3-6 6-2 7-6 (7-5) with a berth in the quarter-finals at stake.
Edmund, ranked 84th, ousted French 13th seed Richard Gasquet in straight sets in the opening round of the tournament.
Fourth seed Rafa Nadal showed he is healthy and ready to challenge for a third US Open title as he rolled into the last 16 with a fist-pumping 6-1 6-4 6-2 win over Russian Andrey Kuznetsov.
Erasing any lingering concerns over an injured wrist that kept him out of Wimbledon, Nadal has made a powerful start to the year's final grand slam, racing into the fourth round without dropping a set.
