Emma Raducanu was bundled out of the Mubadala Citi DC Open in Washington in the semi-finals after losing 6-4 6-3 to Anna Kalinskaya.
The British No 1 matched the Russian early, using her superior serve to pick up five aces.
However, she was frequently unable to take full advantage of her firepower as she failed to convert any of her four break-point opportunities.
This left enough of a window for Kalinskaya to capitalise, clinching the first set before cruising through the second and wrapping up the victory in one hour and 34 minutes.
Raducanu had reclaimed her spot as the top-ranked British woman from Katie Boulter on Thursday when she beat two-time US Open champion Naomi Osaka.
Continuing her return to form in her next match Raducanu had come from a break down in the second set to beat Maria Sakkari 6-4 7-5 that put her into the semi-final with Kalinskaya.
Kalinskaya beat Raducanu in straight sets.
Kalinskaya will now play Leylah Fernandez in Sunday’s final after the the Canadian edged out third seed Elena Rybakina in a marathon encounter that required three tie-breaks for a resolution.
Fernandez prevailed 6-7 7-6 7-6 after three hours and 12 minutes on court.
Meanwhile, a scrappy performance from Australia’s Alex de Minaur was enough to book him a spot in the men’s final with a 6-4 6-3 victory over French lucky loser Corentin Moutet.
The world No 10 overcame 33 unforced errors to wrap up the win in one hour and 44 minutes.
He will face Spain’s Alejandro Davidovich Fokina in the final, after the 12th seed upset American fourth seed Ben Shelton 6-2 7-5.
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