NEW YORK: Lucie Safarova joined the US Open seeds casualty list on Tuesday when the Czech left-hander became the fourth top-10 player to lose in the first round.

Sixth-seeded Safarova slipped to a 6-4, 6-1 defeat to Ukraine’s Lesia Tsurenko, the woman she defeated in the semifinals in New Haven just last week.

“I talked with my coach about what to change. I changed the serve a little bit, made it a more active movement,” said the 26-year-old Tsurenko of the tweaks she made from last week’s clash with the Czech, who had also beaten her in New York in 2013.

“I received pretty bad because she was a lefty. This time I was playing at the back more.”

Safarova, the French Open runner-up, joins seventh seed Ana Ivanovic, eighth-ranked Karolina Pliskova and Carla Suarez Navarro, the 10th seed, in failing to get out of the first round.

With world No.3 Maria Sharapova having pulled out of the tournament through injury, Safarova’s defeat also served to ease Serena Williams’s path to a calender Grand Slam.

World No.2 Simona Halep avoided the upsets when she reached the second round thanks to New Zealand opponent Marina Erakovic retiring with a knee injury.

Halep was leading 6-2, 3-0 when her 99th-ranked rival called it quits, having received a medical timeout for treatment on her right knee at the end of the first set.

Another early winner Tuesday was German 11th seed Angelique Kerber, a 2011 semifinalist, who saw off Romania’s Alexandra Dulgheru 6-3, 6-1.

World No.1s Serena Williams and Novak Djokovic launched title bids in ruthless style late Monday.

Williams, Djokovic cruise

Opening day at Flushing Meadows produced plenty of shock and awe as Djokovic delivered a jaw-dropping performance, speeding past Joao Souza of Brazil 6-1, 6-1, 6-1 as if the Serb had a taxi meter running outside the National Tennis Center.

Williams also played as if she had an appointment to keep as she began her final push toward a calendar year Grand Slam by pounding Vitalia Diatchenko 6-0, 2-0 before the ailing Russian waved the white flag and retired injured.

Eighth seed Rafa Nadal, a two-time US Open champion, needed a bit more time to get the job done, the Spaniard taking nearly three hours to fight off a challenge from 18-year-old Croatian prospect Borna Coric 6-3, 6-2, 4-6, 6-4.

Anna Tatishvili gave the home fans a reason to get excited as the 121st-ranked American qualifier destroyed Pliskova 6-2, 6-1 while Frenchwoman Oceane Dodin kept the upsets trending with 2-6, 7-5, 6-3 victory over Jelena Jankovic, the 21st seed and 2008 US Open runner-up.

Swiss teenager Belinda Bencic, one of just two players to beat Serena Williams this season, strolled past Bulgarian Sesil Karatantcheva to stay on track for a quarter-final showdown with the 33-year-old American.