Serena beats Stephens as Murray cruises

Defending champion through

The defending men's champion Andy Murray and world number one Novak Djokovic also won in straight sets, while 2001 winner Lleyton Hewitt turned back the clock to reach the fourth round for the first time since 2006.

Murray, playing in the middle of a hot and steamy day, needed less than two hours to see off Germany's Florian Mayer 7-6(2) 6-2 6-2 and advance to the fourth round.

Novak Djokovic of Serbia returns a backhand to Joao Sousa of Portugal at the US Open tennis championships in New York, Sept 1, 2013. [Photo/Agencies]

Djokovic was even more ruthless in his center court night match against Portugal's Joao Sousa, cruising to a 6-0 6-2 6-2 win, while 32-year-old Hewitt wore down Russia's Evgeny Donskoy 6-3 7-6(5) 3-6 6-1.

"Obviously when you've been to the top you want to keep playing," said Hewitt, who stunned sixth seed Juan Martin del Potro in the previous round.

"The reason you're playing is for the majors, and for me, Davis Cup as well. That's the reason I'm still playing."

Murray struggled to impose himself on Mayer in the opening set but once he adapted to the humidity and gusting winds it was all smooth sailing.

"It was tough conditions, not tricky. It was very, very humid," Murray said. "I was struggling breathing for most of the match."

Andy Murray of Britain hits a return to Florian Mayer of Germany at the US Open tennis championships in New York, Sept 1, 2013. [Photo/Agencies]

Murray's opponent in the fourth round will be Uzbekistan's Denis Istomin, who beat Italy's Andreas Seppi 6-3 6-4 2-6 3-6 6-1, with Tomas Berdych looming in the quarter-finals.

Berdych, seeded fifth, made the semifinals at last year's US Open and has been in great form at Flushing Meadows this week, reaching the last 16 without dropping a set.

The Czech dispatched Julien Benneteau of France 6-0 6-3 6-2 to set up a fourth round clash with Switzerland's Stanislas Wawrinka, who defeated Marcos Baghdatis of Cyprus 6-3 6-2 6-7(1) 7-6(7).