British number three Heather Watson suffered a 5-7 6-3 7-6 (7-5) semi-final defeat by Pauline Parmentier of France in the WTA event in Quebec, Canada.
The 26-year-old world number 107, seeking her fourth WTA title, took the first set against the eighth seed after battling back from a break down.
But she was soon 3-0 down in the next as world number 69 Parmentier levelled.
Parmentier sealed victory in two hours 35 minutes and will play American Jessica Pegula in Sunday’s final.
Watson had beaten 32-year-old Parmentier in their only previous meeting, a 7-5 6-3 success at the 2012 Osaka quarter-finals en route to her maiden career title.
The British player, bidding to reach her first WTA final since Monterrey 2016, was playing in her first elite level semi-final since Hobart in January.
She had not dropped a set in the Quebec event but it was Istanbul champion Parmentier who reached a second final in one year for the first time.