Novak Djokovic has retired from the US Open with a shoulder injury.
The defending champion had lost the first two sets in his round of 16 match to Stan Wawrinka before pulling out.
The result takes Wawrinka into the quarter-finals of the tournament as he looks for his fourth Grand Slam title.
Meanwhile, Roger Federer eased into the final eight with a straight-set win over David Goffin in just 78 minutes.
Elsewhere, Serena Williams needed medical attention for her ankle as she overcame Petra Martic to reach the quarter-finals for the 16th time.

Abu Dhabi UFC Fight Night ends with Ankalaev fifth-round victory
UFC 333 confirmed for Abu Dhabi in October
Norris takes Hungary pole as Mercedes domination ends
India win second T20 clash in Zimbabwe to take series
Tour de France finale shortened as security forces redeploy to fight wildfires
