Former champion Emma Raducanu is out of the US Open after losing a "rollercoaster" first-round match to Sofia Kenin.

Britain's Raducanu was searching for her first victory in New York since unexpectedly winning the title in 2021 as a teenage qualifier.

She lost in the first round the following year and missed the 2023 tournament as she recovered from wrist and ankle operations.

Raducanu's wait for another win at Flushing Meadows continues after she lost 6-1 3-6 6-4 to fellow Grand Slam champion Kenin.

Kenin, who won the Australian Open in 2020, was on the back foot early in the deciding set but it was Raducanu who faltered, dropping serve at 2-2 before Kenin saw out victory.

"It was a rollercoaster match," Kenin said afterwards.

"Emma is such a tough player and she played some great tennis. I'm just super happy to have won."

Like Raducanu, Kenin has struggled for form since winning her maiden major in Melbourne and reaching the final of the French Open in the same year.

She will face either title contender Jessica Pegula or Shelby Rogers in an all-American second round meeting.