Second seed Simona Halep has admitted that she "wasn't surprised" to see some of the top seeds dropping out early in this year's US Open.

The Romanian's opponent, Marina Erakovic, retired in the second set of her first-round match, ensuring that she reached the second round of the tournament, but sixth seed Lucie Safarova, seventh seed Ana Ivanovic and Karolina Pliskova, who was seeded eighth, all lost in the first round.

The 23-year-old, who has never been past the fourth round at Flushing Meadows, told reporters: "I didn't watch at all but I heard about the results. I mean, all the players who lost yesterday, I think they had a great year at the beginning of the year.

"So it's tough to stay focused an to stay like 100% all the year. I think it's normal. Last year I did the same thing. I played very well at the beginning and middle of the year, and then in US and Asia I didn't play so good. So I wasn't surprised. It's normal."

Halep will face Kateryna Bondarenko of Ukraine in her next match.