Reigning Wimbledon champion Garbine Muguruza advanced while British seventh seed Johanna Konta was ousted Monday at the US Open, where Maria Sharapova's long-awaited return to Grand Slam tennis was finally at hand.
Spanish third seed Muguruza defeated American Varvara Lepchenko 6-0, 6-3 for her first triumph in Arthur Ashe Stadium, which celebrated its 20th anniversary on the first day of New York hardcourt matches.
Muguruza, last year's French Open champion, can reach the US Open third round for the first time Wednesday by defeating China's Duan Ying-Ying.
"Very happy I'm in the second round," said Muguruza. "I've been here so many times and I've never done very well. I will try again and hopefully it will happen."
Serbia's 78th-ranked Aleksandra Krunic upset Australian-born Konta 4-6, 6-3, 6-4, ending her slim hopes at taking the world number one ranking at the tournament.
"I'm happy I had everything together and was able to put some serves in," said Krunic, whose deepest Slam run was to the last 16 here in 2014.
Marin Cilic, the 2014 US Open champion and last month's Wimbledon runner-up, had not played since losing the All England final to Roger Federer due to an adductor strain. 
But the Croatian fifth seed ousted 105th-ranked American Tennys Sandgren 6-4, 6-3, 3-6, 6-3.
"I feel just a little bit rusty," Cilic said. "I need a few matches to get into the rhythm. It's a matter of me getting consistency point after point and match after match and I'll be working on that."
Five-time Grand Slam champion Sharapova was set to face Romania's second-ranked Simona Halep in the night feature, the Russian's first Grand Slam match since serving a 15-month doping ban and only her second on hardcourts.
"I don't think any tennis fan in the world is not going to have that match on," said US 15th seed Madison Keys.
Former world number one Sharapova is 6-0 lifetime against Halep, although she last played the 25-year-old Romanian in the 2015 WTA Finals.
"It's going to be a big challenge, first round of a Grand Slam, to face her," Halep said. "I feel better and I feel that I'm ready to face her again."
Sharapova, whose major titles include the 2006 US Open, tested positive for the banned drug meldonium at the 2016 Australian Open. Her comeback began in April with the aid of wildcards, which drew complaints from many rivals.
"When someone has been banned or out of competition, I think you have to work for it a little bit to go and play your tournaments and not help that much sometimes," Muguruza said Saturday. 
The French Open denied Sharapova a wildcard and she missed Wimbledon with a thigh injury, but US Open officials offered her a wildcard as "a past US champion who needed the wildcard for entry into the main draw," according to a tournament statement.
Sharapova, ranked 146th, played only one hardcourt tuneup match before a forearm injury sidelined her.
Halep has lost three times in three months with a chance to claim the world number one ranking, falling in the French Open final and Wimbledon semi-finals and to Muguruza in the Cincinnati final.
- 'A dark past' at US Open -
Muguruza improved to 17-2 since the start of her London Grand Slam title run, but the 23-year-old Spaniard resists the notion she can be favored with a poor US Open history.
"Coming to US Open and having a dark past in the results, I keep it with low expectations," Muguruza said. "I take every match as a final."
US 10th seed John Isner blasted 22 aces in eliminating France's Pierre-Hugues Herbert 6-1, 6-3, 4-6, 6-3. 
Herbert won 14 points in a row at one stage, including the final 12 of the third set, but Isner took the next 10 and advanced to a second-round affair with South Korea's Chung Hyeon.
"I was playing well out there," Isner said. "He won the third set but I just had to have faith in what I was doing and I'm moving on."