Serbian world number one Novak Djokovic squashed another American hope, pounding Sam Querrey 6-3, 6-2, 6-2 to reach the fourth round of the US Open for the eighth straight year.

Djokovic, a finalist the last four years, winning it all in 2011, improved his record to perfect 8-0 when facing American opponents at Flushing Meadows.

Elsewhere, Andy Murray had his stamina and patience tested at Louis Armstrong Stadium in a third-round battle against Russian Andrey Kuznetsov but came through in good shape.

Hit with cramp during his first-round win, Murray double-faulted to send the match to a fourth set but then swiftly took care of business in a 6-1, 7-5, 4-6, 6-2 win.

Next up for Murray will be ninth seed Jo-Wilfried Tsonga of France, who beat Spain's Pablo Carreno Busta 6-4, 6-4, 6-4.

Tsonga beat Murray in three tight sets in the quarter-finals in Toronto earlier this month on his way to winning the title.

Third seed Stan Wawrinka was handed a walkover when Slovenian Blaz Kavcic was forced out with a right foot injury.

Kavcic, the world number 92, said he had taken an injection to numb his foot but still was unable to play, prompting the withdrawal just before the start of the match.

Source: Reuters