O'Brien could not make the most of her chances in the third set
Britain's Katie O'Brien and Naomi Cavaday both lost in the second round of the DFS Classic in Birmingham.
British number two O'Brien fought hard but ended up losing 7-5 1-6 7-5 to Russian qualifier Yaroslava Shvedova.
"I might have frozen on big points. I was a bit pensive and wasn't swinging the way I'm capable of," she said.
Cavaday, who like O'Brien has a wildcard for Wimbledon, won the first set but faded badly in a 4-6 6-3 6-1 loss to Indian qualifier Sunitha Rao.
O'Brien and Cavaday's defeats leave Mel South as the only Briton left in the event.
O'Brien lost the first set despite her opponent needing treatment for a back problem, but hit back in style to send the match into a final set.
However, Shvedova was always ahead in the decider and came through to win a match which lasted a gruelling two hours.
"Obviously, I'm bitterly disappointed because I didn't play a bad match," added O'Brien.
"I did a lot of things well. I created quite a few opportunities but wasn't quite able to take them."
Top seed Marion Bartoli of France crashed out to Czech player Petra Cetkovska 5-7 6-4 6-0 and sixth seed Sania Mirza lost to New Zealand's Marina Erakovic 6-3 6-0.
Bartoli's exit leaves world number 19 Nicole Vaidisova as the clear favourite to lift the Birmingham title.
She booked a place in the third round with a 6-1 6-3 win over Nathalie Dechy.