British pair Sonay Kartal and Katie Boulter were knocked out in the US Open first round as conditions heated up in New York.
Kartal, who has been managing a knee niggle in recent months, suffered physically in a 6-3 1-6 6-1 defeat against Brazilian 18th seed Beatriz Haddad Maia.
A bizarre deciding set saw a struggling Kartal trail 3-0 before being handed a lifeline when Haddad Maia's movement also became hampered - seemingly down to cramp.
Points became slow and laboured in testing conditions - but neither player refused to give in.
Haddad Maia lost serve for 3-1 as she could barely walk but recovered sufficiently, helped by the vocal support of a boisterous set of Brazilian fans, to serve out a remarkable victory.