Britain's Laura Robson has advanced through to the second round of the US Open after her opponent Ayumi Morita was forced to retire with a shoulder injury.

Robson had claimed the first set 7-6 [7/4] and was leading the second 1-0 when Morita decided she could no longer continue.

Morita has become the second Japanese player to pull out of the event with injury after Kei Nishikori was forced off the court during his match against Flavio Cipolla.

Robson will play either Anabel Medina Garriques or Karin Knapp in the next round.