“It wasn’t my best tennis. It was scrappy tennis but sometimes those kind of matches are a lot of fun and this was one of those days.”

The 30-year-old Russian became the first player into the third round where she will face Russian-born US teen wild card Sofia Kenin.

Sharapova, whose five major titles include the 2006 US Open, tested positive for meldonium at the 2016 Australian Open, her most recent grand slam appearance until this week.

“Every day I have the chance to play out here at the US Open is a special day and I’ll look forward to the next one,” Sharapova said.

Sharapova, ranked 146th, played only one US Open warm-up match because of a forearm injury but wore down Halep and Babos to prove she is a threat for a deep run.

German fourth seed Zverev, whose five ATP titles this year include a win over Roger Federer in this month’s Montreal final, fell to world No 61 Croatian Borna Coric 3-6, 7-5, 7-6 (7-1), 7-6 (7-4).

“He had a most unbelievable year where he won basically everything,” Coric said. “It does mean a lot to me to win this match.”

Coric, who next faces South African Kevin Anderson for a spot in the last 16, was one point from being pushed to a fifth set before winning five in a row to take the 12th game of the final set.

“I was just thinking to keep the points shorter,” Coric said. “And yeah, I was a little bit lucky.”

Zverev’s exit left US 10th seed John Isner the top-ranked player in his draw quarter and Croatian fifth seed Marin Cilic, coming off a Wimbledon runner-up effort, the best in his half of the draw.

Cilic, the 2014 US Open winner, reached the third round by beating Germany’s Florian Mayer 6-3, 6-3, 6-3.

Kyrgios, the 14th seed and highest-ranked obstacle in Federer’s quarter-final path, hurt his right shoulder in a 6-3, 1-6, 6-4, 6-1 first-round loss to world No 235 Aussie compatriot John Millman.

“Early in the third set I hit one serve and I never felt the same after that,” Kyrgios said. “Something didn’t feel right in my arm.”

Kyrgios, 22, beat Rafael Nadal two weeks ago on the way to the biggest final of his career at the ATP Cincinnati Masters before falling to Grigor Dimitrov.

Kyrgios grabbed his right shoulder after a serve in the fourth game of the third set, telling a physiotherapist his woes during a medical timeout.

“One serve and my arm is totally dead. It’s so dead and numb. It’s incredibly weak,” said Kyrgios.

After his last available treatment, Kyrgios dropped eight of the last nine games to Millman, who missed nearly eight months with a hip injury.

“Nick’s shoulder deteriorated as the match went on,” Millman said after his first US Open triumph. “It’s a victory but slightly hollow.”

Austrian sixth seed Dominic Thiem finished off Aussie Alex de Minaur 6-4, 6-1, 6-1. Thiem is the highest-ranked rival to Federer and Nadal on their side of the draw.

“I’m not in the first row of favourites, maybe in the second, so I can play calm,” Thiem said.

Russian eighth seed Svetlana Kuznetsova, the 2004 US Open champion, rescued three match points in defeating 67th-ranked Czech Marketa Vondrousova 4-6, 6-4, 7-6 (7-2) to reach the second round.

Kuznetsova is among seven women who could become world number one after the US Open. So is Fourth seed Elina Svitolina of Ukraine, who held off No 42 Czech Katerina Siniakova 6-0, 6-7 (5-7), 6-3.

Also sustaining top spot hopes was seven-time grand slam champion Venus Williams, the US ninth seed who beat France’s Oceane Dodin 7-5, 6-4. This year’s Wimbledon and Australian Open runner-up is the field’s oldest woman at 37.