Harriet Dart and Francesca Jones both fell to seeded players as British interest in the US Open singles ended in the second round.
Dart said she felt “under the weather” during her 6-2 6-2 defeat by Czech 25th seed Marie Bouzkova as temperatures reached around 30C in New York.
Her loss meant Jones was the last Briton standing in either singles draw, and she acquitted herself well before falling 6-4 6-4 to 14th seed and rising American star Iva Jovic.
Nine British players competed in the US Open main draws – the most since 1981 – with four coming through qualifying.
Five of them reached the second round, but Jacob Fearnley was the only player to win a set as they all fell to seeded players.
Lucky loser Fearnley fell in four sets to 27th seed Tomas Martin Etcheverry, while qualifier Toby Samuel was beaten by 18th seed Jiri Lehecka.
Katie Boulter lost to Wimbledon runner-up Karolina Muchova in only 58 minutes on Wednesday.
In the men’s draw, Cameron Norrie, Arthur Fery, Harry Wendelken and Jan Choinski exited in the first round.
Jones, ranked 90 places lower than Jovic, made the American work for one hour and 54 minutes to reach the third round.
Humid conditions meant both players frequently dashed to the back of the court between points to dry their hands and face.
It was Jovic who started on the front foot, opening up a double break and a 3-0 lead as the 18-year-old controlled the rallies with some deep hitting from the baseline.
Jones snatched a break back and kept in touch with Jovic – but she could not make the most of a break point as Jovic served for the set.
After wrapping up the opener, Jovic raced into a 4-1 lead in the second, only to once again be dragged back by Jones.
The Briton saved three match points on her own serve but Jovic produced one of her best service games to seal victory and set up a meeting with good friend Alexandra Eala.