Konta, a quarter-finalist at last year's US Open, was beaten 6-2, 6-7 (5/7), 4-6 in a hard-fought contest that lasted just under three hours.

Konta joins top seed Karolina Pliskova and 10th seed Garbine Muguruza as the biggest casualties from early round play this week.

Cirstea, ranked 77th in the world, will now play 20th seed Karolina Muchova in the third round.
It is only the third time in 11 appearances in the main draw at the US Open that the 30-year-old Cirstea has reached the third round.

The Australian-born Konta had looked to be in control after racing through the first set, but was unable to counter as Cirstea responded strongly in the second, aided by a strong serve which saw her finish with eight aces.

Konta had no complaints with the defeat afterwards.

"I think my level was a lot higher than hers in the first set," she said. 
"But she's a great player. She has had some pretty amazing results also in the past in her career. She's capable of playing some very good tennis.

"She obviously raised her level. We were battling kind of toe-to-toe really. She just was better in the end."