NEW YORK -- Novak Djokovic needed all of 15 minutes to take the first five games against Sam Querrey, sending the top-seeded Serb on his way to the US Open's fourth round for the eighth year in a row.
Djokovic's routine 6-3, 6-2, 6-2 victory Saturday put him in the round of 16 at a 22nd consecutive Grand Slam tournament.
Djokovic counts the 2011 US Open among his seven major titles and has played in the past four finals at Flushing Meadows.
He had no trouble handling the big serves of Querrey, breaking the former top-20 player seven times in the 1-hour, 26-minute match.
Murray, who dealt with severe cramping in his first-round victory Monday, awkwardly pulled up after some shots in the third set, wincing and grimacing occasionally. He double-faulted to get broken and drop that set.
But Murray went up a break at 2-1 in the fourth and held on from there.
"I ate properly, I drank properly, I felt a lot better today," he said.
His win sets up an intriguing fourth-round matchup with No. 9 Jo-Wilfried Tsonga, who overcame tough winds in the Grandstand to beat Pablo Carreno Busta 6-4, 6-4, 6-4. His prediction: "I will come on the court as a fighter."
Murray, the 2012 champion at Flushing Meadows, has made the fourth round of the US Open seven times in the last 10 years.
He has not reached the final at any tournament since winning Wimbledon in July 2013.
The 10th-seeded Nishikori, who has not made it past the fourth round in five previous US Open appearances, showed no sign of a big toe injury that hampered his preparations for Flushing Meadows.
The Associated Press contributed to this report.