Making her first appearance at a major event since the 2016 Australian Open due to her 15-month doping suspension, the former world number one defeated Halep 6-4, 4-6, 6-3 in front of a sell-out crowd in NY.
Sharapova was banned from tennis for 15 months after testing positive for meldonium at the 2016 Australian Open and she has largely stuttered during her comeback due to various injury problems. Sharapova won the tournament in 2006, the second major title of her career.
"Maybe I'm more of a favourite, I guess", Muguruza said.
Ranked 146th, Sharapova's appearance at the U.S. Open is by virtue of a gifted wild-card entry. Halep also reached the final of the 2017 French Open, but lost to Jeļena Ostapenko, who became the first unseeded player to win the tournament since 1933.
"I had no idea what she looked like, who she was, anything", Williams said of Kuzmova.
Cilic is the only one of these players who has won a Grand Slam before but has not played since he suffered an adductor injury during Wimbledon. Her vast experience at the US Open will be critical for her to make a run this year. "So I think it's really interesting, great time for women's tennis".
Asked what had she learned from a match that felt more like a final than an opening-night encounter, Sharapova said: "That behind this black dress with Swarovski crystals this girl has a lot of grit and she is not going anywhere".
In the second set alone, Halep staved off five break points before clinching the 10th game and forcing a third set. She wept tears of joy, as well as waved and blew kisses to the crowd as she mouthed "Thank you".
Before the game, singer Shania Twain performed one of her impressive songs at the US Open opening ceremony to open what is expected to be one of the most interesting Grand Slams. She made it very tough for me to be able to get any easier points.
It was the type of all-or-nothing assault that has served her well since she first burst on the scene with a 2004 Wimbledon title. Since I've come back, I feel like I'm on a team.
34 of Wozniacki's 99 major wins have come in NY, where she is a two-time runner-up and has reached at least the semifinals on five occasions.
The blockbuster matchup was always assured to be the headline match of the first week in NY, but no one could have foreseen Sharapova's blistering form after an arm injury cut short almost her entire summer hard-court season. "I know it's going to be very hard with obviously so many girls playing for this position, but I think I have a good chance to stay there if I play well".