Garbine Muguruza, the reigning Wimbledon champion, defeated Varvara Lepchenko of the United States 6-0, 6-3 for her first triumph at Arthur Ashe Stadium, which is celebrating its 20th anniversary.

"Very happy I'm in the second round," Muguruza said. "I've been here so many times and I've never done very well. I will try again and hopefully it will happen."

The 23-year-old Spaniard improved to 17-2 since the start of her Wimbledon title run, a stretch that also included a crown at Cincinnati, in the last major US Open tuneup.

Cilic advances

On the men's side, the fifth seed and 2014 champion, Marin Cilic, advanced to the second round with a 6-4, 6-3, 3-6, 6-3 win over Tennys Sandgren of the United States.

The Croatian, who was playing his first match since losing the Wimbledon final to Roger Federer, is to face Germany's Florian Mayer for a place in the last 32. Mayer beat Rogerio Dutra Silva of Brazil 7-5, 0-6, 6-3, 6-4 in his first-round contest.

Germany's Mischa Zverev fought back from a set down to beat Thai-Son Kwiatkowski in three-and-a-half hours, 7-6 (5), 4-6, 4-6, 7-5, 6-3. Kwiatkowski from North Carolina had won the NCAA college championship in May, giving him an entry to the US Open.

Zverev, who reached a career high world ranking of 25 in July, hit 11 aces and won 72 percent of his first-serve points. He next faces Frenchman Benoit Paire.

Sharapova's Grand Slam comeback                     

The showcase match of the day came with the first night match when Maria Sharapova faced Romania's second-ranked Simona Halep. It was the Russian star's first Grand Slam match since coming back from a 15-month doping ban.

Sharapova's five Grand Slam titles included the 2006 US Open, and the organizers said in a statement that they had granted her a wild card as "a past US champion who needed the wild card for entry into the main draw."

After a tight first set which Sharapova won 6-4, she looked ready to move ahead in the second set but Halep pinned her back to take it 6-4.

After breaking Halep's fragile serve, Sharapova served for the match at 5-3 in the third set and sank to her knees with tears in her eyes after winning the final point. She hit 60 winners to Halep's 15 during the 2 hours, 44 minutes of the match.

 

Can Zverev make an impact?

German fans are hoping that Mischa's younger brother Alexander Zverev, who beat Federer in the final of the Rogers Cup in Montreal earlier this month to take his fifth title of the year, can make an impact in New York.

But the 20-year-old fourth seed was made to work hard in his first round match against Grand Slam debutant Darian King of Barbados. Zverev took the first set on tiebreak, before eventually holding on a straight sets 7-6, 7-5, 6-4 victory in a match that lasted until after 02:00 in the morning.

Earlier, in addition to Mayer, Germany's Julia Görges advanced, beating her compatriot Annika Beck 6-1, 6-0. Another German woman, Carina Witthöft was knocked out in the first round, losing to Anastasija Sevastova of Latvia.

Seven-time Grand Slam champion Venus Williams, this year's Australian Open and Wimbledon finalist, won 6-3, 3-6, 6-2 against Viktoria Kuzmova, a 19-year-old qualifier from Slovakia, ranked 135th. The win took the 37-year-old Williams' record in the US Open to 19-0 in first round matches.

The defending women's champion, Germany's Angelique Kerber, doesn't play until Tuesday, when she is to face Naomi Osaka of Japan.

The titleholder on the men's side, Switzerland's Stan Wawrinka, is one of a number of stars, including his opponent in last year's final, Novak Djokovic, who haven't made it to this year's edition of the tournament. Notable others include Andy Murray, Kei Nishikori and Canada's Milos Raonic.

jm, pfd/cmk (AP, dpa)