World number four Petra Kvitova has fallen to a third-round 6-4 6-4 defeat at the US Open to Serbia's Aleksandra Krunic.

The first set was incredibly tense and Kvitova was unable to handle the pressure at 4-4 as a double fault handed Krunic the break she needed, with the young Serbian going on to serve out the set.

Krunic broke again in the second set to make it 4-2 and looked certain to take victory, but Kvitova broke back immediately to level to second set at 4-4.

Once more though, her nerves at the business end of the game failed her and she dropped her serve before Krunic made no mistake in serving out the match to progress to the next round.