Top seed Novak Djokovic and defending champion Andy Murray both saw off challengers as they marched through into the second week of the US Open on Sunday.

Novak Djokovic, the tournament number one, defeated Joao Sousa 6-0, 6-2, 6-2 as the Portuguese made his first appearance in the pressure-cooker ambience of the Ashe court at night.

Murray, seeded third, overcame daytime heat and humidity to move ahead towards the business end of the final major of the season, beating German Florian Mayer 7-6 (7-2), 6-2, 6-2.

The reigning champion in New York and Wimbledon had to resort to the ice towel at changeovers in the gruelling conditions to score his third-round victory in just over two hours, finishing with seven aces and 42 winners.

But Murray said he needs quicker starts if he’s to continue his winning ways. “I need to get going a bit quicker,” he said. “I was a bit slow out of the blocks. Once I got my feet into the right position, I was hitting the ball fine. But a faster start would help me. But I was struggling breathing for most of the match.”

Murray brought a 2-0 record over Mayer - both wins on clay - into the contest. The seed has now won 11 straight Grand Slam third—round matches.

The winner said he felt the weather conditions as well as the quirky game of Mayer.

“He’s a tricky opponent who plays some strange shots. It was tough to get a win in three sets against a guy like him. The weather was hot, but they tell us thunderstorms are coming and it will hopefully cool down. Hopefully some of the humidity will go away,” said Murray, who trains in similar conditions each December at his base in Miami.

Murray will play for the quarter-finals against Denis Istomin, a winner over Italian Andreas Seppi 6-3, 6-4, 2-6, 3-6, 6-1. Djokovic, who has barely been tested so far, faces Spaniard Marcel Granollers, who rallied from 1-4 down in the fifth set to beat Tim Smyczek 6-4, 4-6, 0-6, 6-3, 7-5.

The result means that there will be no American man in the New York fourth round for the first time ever.

Czech fifth seed Tomas Berdych, a 2012 semi-finalist, advanced into the fourth round with his defeat of Frenchman Julien Benneteau 6-0, 6-3, 6-2.

“Today it was good,” said Berdych. “Finally I managed to stay focused from the first point till the last. I didn’t have any ups and downs. I just took all my chances and won in straight sets.” Swiss ninth seed Stanislas Wawrinka duelled for more than three hours before beating former grand slam finalist Marcos Baghdatis 6-3, 6-2, 6-7 (1-7), 7-6 (9-7), with the winner managing 11 aces to 16 for his losing opponent.

Wawrinka produced 53 winners to 50 unforced errors and broke on five of 15 chances to next play Berdych.

“It’s always tough to play against him; we’ve had some great battles together. I need to adapt a little bit my game, because he’s so powerful, so I need to change a little bit.

“But he’s not really happy to play against me, he doesn’t like my game. I know if I’m fit and if I play well, I have some chances.” Veteran battler Lleyton Hewitt continued his run of form, beating Russian Evgeny Donskoy 6-3, 7-6 (7-5), 3-6, 6-1 to reach the fourth round of a major for the first time since the 2012 Australian Open. Russian Mikhail Youzhny beat, the 12th seed, 6-3, 6-2, 2-6, 6-3.

In women’s play, top seed Serena Williams took revenge for a January loss to Sloane Stephens, defeating the young American 6-4, 6-1. Williams will play Spain’s Carla Suarez Navarro, who put out eighth seed Angelique Kerber of Germany 4-6, 6-3, 7-6 (7-3).

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