Novak Djokovic and Rafael Nadal advanced to the second round of the men's competition, while Serena Williams had an easy victory in Day 1 of the 2015 US Open on Monday at Flushing Meadows.

Djokovic, who is eyeing the 10th Grand Slam title of his career, did not have troubles in his tournament opener, as he cruised to a 6-1, 6-1, 6-1 win against Joao Souza of Brazil.

The top-seeded Serb, who won the US Open in 2011, needed just 71 minutes to dispatch Souza and advance to the second round, where he will face Andreas Haider-Maurer of Austria, who escaped with a five-setter win against Vasek Pospisil of Canada.

Meanwhile, Rafael Nadal made his return to Flushing Meadows on Monday, and it was a successful comeback, as he scored a 6-3, 6-2, 4-6, 6-4 victory against Borna Coric of Croatia.

Nadal, a two-time US Open champion, had a strong performance in the first two sets of the match, but was bothered by stomach problem in third set and felt dehydrated.

Nadal dropped the third set, but managed to bounce back in the fourth to take the victory. The eighth-seeded Spaniard, who missed last year's tournament because of a wrist injury, said that he will be back to full strength in the second round, where he will face Diego Schwartzman of Argentina.

Defending champion Marin Cilic also earned a spot in the second round with a hard-earned 6-3, 7-6, 7-6 victory against Guido Pella of Argentina, while 2014 runner-up Kei Nishikori of Japan took a 6-4, 3-6, 4-6, 7-6, 6-4 upset loss to unseeded Benoit Paire of France.

In the women's side, defending champion Serena Williams was anxious heading into her tournament opener, but the top-seeded superstar showed no signs of nerves against Vitalia Diatchenko of Russia.

Williams moved on to the next round with a 6-0, 2-0 victory in just less than 30 minutes after the Russian failed to continue. According to ESPN, the 86th-ranked sustained a foot injury.

Williams, who is looking to sweep all Grand Slam titles this year and win her fourth consecutive US Open title, will next face Kiki Bertens of Netherlands, who scored a 3-6, 6-4, 6-2 win against Mirjan Lucic-Baroni of Croatia.

Seventh-seeded Ana Ivanovic of Serbia also booked a spot in the second round with a 6-3, 3-6, 6-3 win against Dominika Cibulkova of Slovakia.

Complete 2015 US Open Day 1 results are available on this link from the tournament's official website, while match highlights can be viewed here.

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