US Open PHOTOS: Zvarev struggles, Cilic, Muguruza march on; Halep stunned

Images from Day 1 at the US Open played at Flushing Meadows in New York on Monday

Alexander Zverev battled into the early hours of Tuesday to defeat a surprisingly troublesome Darian King 7-6(9), 7-5, 6-4 at the US Open.

The fourth-seeded German got all he could handle in the first set from the little-known 25-year-old, who made it through qualifiers to become the first player from Barbados to compete in a grand slam.

Dressed in knee-high socks and striped headband that recalled a 1970's-era Bjorn Borg, Zverev looked out of synch early in the match, the booming serve that helped bring him five titles this year lacking its usual punch.

The German was uncharacteristically wasteful in a one hour, 21 minute first set, committing 31 unforced errors, before going on to draw first blood.

"Obviously Darian came out playing really good tennis and I couldn't find my rhythm," he said on court after he finished the nearly three hour match with an overhead smash.

"It was an entertaining first set."

Next up for Zverev is fellow 20-year-old Borna Coric of Croatia. 

 Cilic fights past USA's Sandgren 

Croatia's Marin Cilic started strong and hung on to win his first match since his emotional defeat in the Wimbledon final, besting American Tennys Sandgren 6-4, 6-3, 3-6, 6-3 on Monday to reach the second round of the US Open.

The 2014 US Open champion moved well throughout the nearly three-hour match and appeared unhindered by the adductor injury and foot blisters that ailed him during his straight sets loss to Roger Federer at the All England Club.

"I need a few matches to get in the rhythm. I was hitting some good shots and then making some unforced errors."

Cilic ended with 57 unforced errors, many coming from his wobbly forehand, compared to 55 winners.

Sandgren was composed throughout the match but appeared to tire as the match wore on.

The 26-year-old American was ultimately unable to overcome the early deficit and Cilic's powerful serve and punishing groundstrokes.

Next up for Cilic in the second round is German Florian Mayer, a 7-5, 0-6, 6-3, 6-4 winner over Brazil's Rogerio Dutra Silva.

Sharapova stuns Halep

Former world number one Maria Sharapova made a big return to Grand Slams after a 15-month doping ban, knocking out second-ranked Simona Halep 6-4, 4-6, 6-3 at the US Open.

The 30-year-old Russian, who had only one hardcourt warm-up match due to a forearm injury, played 60 winners with 64 unforced errors, in a tension-packed thriller at Arthur Ashe Stadium.

"I just thought this was another day, another opportunity, another match but this was so much more," Sharapova said.

"You sometimes wonder why you put in all the work and this is exactly why."

Wozniacki rolls through first round

Fifth seed Caroline Wozniacki capitalised on 41 unforced errors by Romanian Mihaela Buzarnescu to cruise to a 6-1, 7-5 win in their first round meeting at the US Open on Monday.

The 29-year-old Buzarnescu, who was playing in her first-grand slam match, was overwhelmed by the Dane's powerful baseline game in the first set.

She came out with more energy in the second and the two exchanged service breaks to get to 4-4.

However, the Romanian became frustrated as she struggled with accuracy and the lefty sent a two-handed backhand long to hand Wozniacki a trip to the second round.

"The first round is always difficult, you just want to get into the tournament," Wozniacki said in an on-court interview.

The win was the former world number one's 100th grand slam match victory.

Muguruza powers past Lepchenko 

Wimbledon champion Garbine Muguruza notched up her first ever victory on Arthur Ashe Stadium with a 6-0, 6-3 win over American Varvara Lepchenko at the US Open on Monday.

Despite winning two grand slam titles, Muguruza has never felt at home at Flushing Meadows as she has never advanced past the third round here.

"I have been here so many times and I've never done very well," said the Spaniard.

"She started a little nervous and I started well. Then it got more equal and became a good fight."

Lepchenko struggled with her accuracy on the partly-cloudy morning, committing 22 unforced errors to Muguruza's 11.

The 23-year-old Muguruza was aggressive throughout, frequently coming to the net and using her powerful ground strokes to push Lepchenko into awkward court positions.

Muguruza will next face either American Claire Liu or Duan Ying-ying of China.

Kvitova wears down Jankovic to reach round two

Twice Wimbledon champion Petra Kvitova scraped into the second round of the US Open by beating former world number one Jelena Jankovic of Serbia 7-5, 7-5.

The Czech 13th seed, in search of top form after a mediocre build-up to the year's final Grand Slam, struggled to adapt to Jankovic's counter-punching style but eventually wore down the 2008 runner-up to set up a meeting with France's Alize Cornet.

Kvitova, who returned to competition inh May five months after being stabbed in her hand by an intruder at her home, won a first set that featured three breaks of serve as both players struggled to find their range in Louis Armstrong Stadium.

She rallied back from 2-0 down in the second set but dropped serve again in the seventh game. However, Kvitova regained her composure to win four consecutive games and secured the win on her first match point with a sizzling forehand winner down the line.

Confident Venus marches forth

Mike SegarVenus Williams led the American charge into round two on Monday with a 6-3 3-6 6-2 win over Viktoria Kuzmova of Slovakia.

The 37-year-old, who last won the title in New York in 2002, is high on confidence after reaching two grand slam finals in 2017, in Australia and at Wimbledon.

“I feel like my game always rises a lot in the bigger events,” Williams told a news conference. “That's what I feel like, like I'll be ready to play when push comes to shove.”