Gold medalist Puig out but Vinci, Kerber and Wozniacki all through to second round of US Open

China's Zheng Saisai eased into the second round as she beat Monica Puig, the winner of gold at the 2016 Rio Olympics 6-4, 6-2 at Flushing Meadows.

Puig, the current world no.34 was told in the press before the game that she had to use the tournament to prove her success in Rio was no fluke, but she couldn't find a way past Saisai, currently ranked 60.

She will face either Hsieh Su-wei or Kateryna Bondarenko in the next round, with a potential third round match against Garbine Muguruza on the cards.

Italy's Roberta Vinci, the woman who knocked Serena Williams out of the 2015 US Open semi-finals, breezed into the second round.

Vinci had the honour of kicking the tournament off on Arthur Ashe court, with last year's winner Flavia Pennetta having retired.

And she justified her billing with a fine display to beat Germany's Anna-Lena Friedsam 6-4 6-2.

Friedsam was a tough draw for seventh-seeded Vinci: the German is ranked 46th in the world, and is 11 years younger.

But Vinci came through in just one hour and eight minutes to earn a match against either Christina McHale, who beat Germany's Mona Barthel 6-2 6-2.

"It's a dream to come back here... this court is incredible, it's a special court for me," Vinci told ESPN after the match, to the delight of the crowd.

"Nervous at the beginning, but now I'm happy," she added.

Australian Open champion Angelique Kerber made it into the second round of the US Open without losing a game as her opponent Polona Hercog retired injured.

Hercog had lost the opening set 6-0, and after losing the opening game of the second set admitted that she couldn't continue.

"To be honest, it's never the way I would like to finish the match, but I went out there to feel my rhythm and start the tournament well," said Kerber, who improved to 49-4 this season.

"I played the first set really good, so this is what I will take from this match, that I'm playing my tennis.

"For me, it's always tricky the first few rounds. So it's always good to have the first round done."

Former champion Svetlana Kuznetsova put in a consummate performance to beat Italy's Francesca Schiavone, losing just three games in a 6-1 6-2 win.

Kuznetsova, the ninth seed, has not made a Grand Slam final in over seven years, but returned to the world's top 10 for the first time since 2010 by making the fourth round at Wimbledon.

She looked in outstanding form on Monday with her victory, belying her 31 years - though given that the last two champions of the tournament have been in their thirties (Serena Williams and Flavia Pennetta) perhaps we should expect nothing less from the veterans.

Former world number one Caroline Wozniacki came through a very tough opening match at the US Open.

The Dane lost the opening set before turning things round to beat Taylor Townsend 4-6 6-3 6-4.

It is the first Grand Slam match win of 2016 for Wozniacki, who has made the final in New York twice - in 2009 and 2014.

Aug 30 (Gracenote) - Results from the U.S. Open Women's Singles Round 1 matches on Monday

Alison Riske (USA) v 8-Madison Keys (USA) 4-6, 7-6, 6-2

12-Dominika Cibulkova (Slovakia) beat Magda Linette (Poland) 6-2 6-3

Lesia Tsurenko (Ukraine) beat 21-Irina Begu (Romania) 6-0 6-4

3-Garbine Muguruza Blanco (Spain) beat Elise Mertens (Belgium) 2-6 6-0 6-3

Wang Yafan (China) beat Alison Van Uytvanck (Belgium) 6-3 7-6(4)

Duan Yingying (China) beat Maria Sakkari (Greece) 6-4 4-6 6-3

Anastasija Sevastova (Latvia) beat Anna Karolina Schmiedlova (Slovakia) 6-3 6-3

Yulia Putintseva (Kazakhstan) beat Sabine Lisicki (Germany) 6-1 6-2

Naomi Osaka (Japan) beat 28-CoCo Vandeweghe (U.S.) 6-7(4) 6-3 6-4

Catherine Bellis (U.S.) beat Viktorija Golubic (Switzerland) 6-2 6-3

Shelby Rogers (U.S.) beat 27-Sara Errani (Italy) 6-4 7-6(3)

Christina McHale (U.S.) beat Mona Barthel (Germany) 6-2 6-2

9-Svetlana Kuznetsova (Russia) beat Francesca Schiavone (Italy) 6-1 6-2

Mirjana Lucic-Baroni (Croatia) beat Alize Cornet (France) 6-4 6-1

Caroline Wozniacki (Denmark) beat Taylor Townsend (U.S.) 4-6 6-3 6-4

Cagla Buyukakcay (Turkey) beat Irina Falconi (U.S.) 6-2 6-1

2-Angelique Kerber (Germany) beat Polona Hercog (Slovenia) 6-0 1-0 (Hercog retired)

Andrea Petkovic (Germany) beat Kristina Kucova (Slovakia) 7-6(3) 6-3

24-Belinda Bencic (Switzerland) beat Samantha Crawford (U.S.) 6-7(6) 6-3 6-4

14-Petra Kvitova (Czech Republic) beat Jelena Ostapenko (Latvia) 7-5 6-3

Carina Witthoeft (Germany) beat 30-Misaki Doi (Japan) 6-4 6-1

7-Roberta Vinci (Italy) beat Anna-Lena Friedsam (Germany) 6-2 6-4

13-Johanna Konta (Britain) beat Bethanie Mattek-Sands (U.S.) 6-3 6-3

22-Elina Svitolina (Ukraine) beat Mandy Minella (Luxembourg) 6-7(5) 6-0 6-2

Monica Niculescu (Romania) beat 18-Barbora Strycova (Czech Republic) 6-3 6-7(3) 6-1

Lauren Davis (U.S.) beat Aliaksandra Sasnovich (Belarus) 6-2 4-6 7-5

Kayla Day (U.S.) beat Madison Brengle (U.S.) 6-2 4-2 (Brengle retired)

Kateryna Bondarenko (Ukraine) beat Hsieh Su-Wei (Taiwan) 6-0 7-5

Ana Bogdan (Romania) beat Sorana Cirstea (Romania) 0-6 7-5 6-2

Zheng Saisai (China) beat 32-Monica Puig (Puerto Rico) 6-4 6-2

Tsvetana Pironkova (Bulgaria) beat Virginie Razzano (France) 6-1 6-2

Evgeniya Rodina (Russia) beat Danielle Collins (U.S.) 6-1 6-2