Defending champion Novak Djokovic reached the US Open last 16 in just 32 minutes on Friday when Russian opponent Mikhail Youzhny retired at 2-4 down in the first set.
The 34-year-old Youzhny had needed treatment on a left leg injury after five games and called it quits just a game later.
World number one Djokovic had reached the third round on a walkover when Jiri Vesely withdrew from their second round clash.
The top seed had needed four sets to beat Jerzy Janowicz in the first round on Monday.
KEYS LEAVE IT LATE
Madison Keys mounted an epic final set comeback to keep her title dreams alive.
The eighth-seeded American won the latest-ever finishing women’s match at the tournament on Monday when she completed victory over compatriot Alison Riske at 1:48am.
On Friday, the 21-year-old was involved in more drama when she rallied from 1-5 down in the final set to defeat Japan’s Naomi Osaka 7-5, 4-6, 7-6 (7/3).
The 18-year-old Osaka was reduced to tears as she twice served for the match but choked under the immense pressure.
“This is the greatest comeback of my career, hands down,” said Keys who will face two-time runner-up Caroline Wozniacki for a quarter-final spot.
PUT A SOCK IN IT
Jack Sock sent 2014 champion Marin Cilic crashing out in spectacular style, blowing the Croatian off the court.
Sock, the 26th seed, reached the fourth round for the first time by knocking out a cramping seventh seed Cilic, 6-4, 6-3, 6-3 in tie where he did not face a single break point.
The 23-year-old, whose last two appearances at the US Open had ended in retirements, goes on to face French ninth seed Jo-Wilfried Tsonga (who got past Kevin Anderson in four sets).
Sock had defeated Cilic from two sets down in America’s losing effort in the quarter-finals of the Davis Cup.