Anastasia Sevastova qualified for the Kremlin Cup semi-final after returning from a late set-up against Russian rival Vera Zvonareva of the qualifiers to a 4-6, 7-5, 6-3 victory.
The Latvian, who has also won the previous two rounds in three weary sets, kept her hopes of entering the top 10 women's world championships for the first time after making a strong show against former world number two Zvonareva.
"I think the game was fantastic," said Sevastova, who is now 11th in the world.
"Zvonareva started the attack.
Sevastova, 28, broke her Russian opponent midway through the first set to advance 4-3 but the experienced Zvonareva, who managed to control the balls on the net, won the next three games.
After a slight lead in the second set thanks to the shots and strong blows, Sevastova pressed for a 3-3 draw in the third set before the game was settled.
Sevastova will face her rival Anas Gaber, who defeated Estonia's Annette Contavet 7-5, 6-1 to become Tunisia's first female player to qualify for the semi-finals of the Women's League.
Britain's Johanna Kunta made her way to the semifinals for the second time in a volatile season after beating 6-2 2-6 7-6 on Belarus's No. 31 Belarusian Alixandra Sassenovic.
Conta, who dropped to 44th in the world, will face Russian Daria Castackina, who defeated compatriot Anastasia Pavlyuchenkova 6-4, 6-3.
