Conditions can often be difficult at the US Open, which takes place in the New York summer and regularly has matches played in oppressive heat.

This was one of those occasions. Temperatures hit 35C at Flushing Meadows as Dart faced Kostyuk in the maelstrom of the mid-afternoon sun.

Both players regularly needed ice towels to cool down and, looking flustered, struggled to stay composed in an erratic match which lacked quality.

Double faults were thrown around regularly from each server, including one by Kostyuk on a set point in the tie-break, with another from Dart also handing over the first break of the second set.

Wild returning was another feature of a match which, particularly in the first set, was a difficult watch.

Dart will become the British number two after the US Open, climbing above Emma Raducanu, when she rises the rankings on the back of her first-round victory over France's Chloe Paquet.

Beating Kostyuk would have moved Dart into the top 60 and secured one of the biggest wins of her career by ranking.

She made a sharp start but was left to rue not being clinical enough in a scrappy first set and punishing Kostyuk, whose piercing roar at securing the lead indicated her own angst.

A suspect second serve has been something which Dart's opponents have pounced on. Here, she punished herself with the volume of double faults.

Landing 46% of first serves in the match and winning just 28% of second-serve points, also starkly illustrated where the problems lie.

Dart looked close to tears at the start of the second set and continued to gesticulate towards her team, which was led by mum Susie who has been coaching her in New York.

Reassuring words could not help a demoralised Dart settle back into her rhythm and the fight was sucked out of her.

Kostyuk, who had played far below her ranking, suddenly relaxed as a result of her opponent's problems and wrapped up a victory which was more comfortable than it should have been.