Former champions Anastasia Pavlyuchenkova and Jelena Jankovic advanced to a second round showdown at the Kremlin Cup on Tuesday.
Pavlyuchenkova, the 2014 winner and seeded seventh, battled through a tough three-set first round clash with Czech Katerina Siniakova.
The Russian, ranked 23rd, won 7-6 (7/2), 5-7, 7-5 in two hours 46 minutes, to chalk up her third win over the 20-year-old Siniakova in as many meetings.
Pavlyuchenkova will face Jankovic for a place in the last eight after the 2008 winner from Serbia eased past Jelena Ostapenko of Latvia 6-3, 6-3 in 74 minutes.
"Overall it was tougher than the scoreline suggests," Jankovic told AFP.
"It was a bit unusual with so many breaks and it was quite difficult for me to hold my serve. But my good return made the difference today.
"Of course I would love to repeat my 2008 success here as it's always my goal - to win the tournament that I'm playing."
Pavlyuchenkova, who is seeking a career ninth and season's first title in Moscow, took the opening set in a tiebreak after 51 minutes, while Siniakova fought back from 3-0 down in the second to level after one hour 52 minutes on court.
The deciding set was a mirror reflection of the second as Pavlyuchenkova overcame a three-game deficit to claim her second-round spot.
Earlier, Croatian lucky loser Ana Konjuh, ranked 58th, produced the first upset of the tournament beating sixth seeded Czech Barbora Strycova 6-4, 1-6, 6-2.
"I'm really pleased to get the win," the 18-year-old Konjuh said. "It wasn't easy after losing in qualifying but today thankfully I played my own style of tennis. I was more aggressive than her and that was the key."
In the ATP section, Italy's Paolo Lorenzi, the seventh seed, cruised into the second round with a 6-4, 6-4 win over a compatriot Federico Gaio, while sixth seeded Spaniard Pablo Carreno Busta ousted Austria's qualifier Jurgen Melzer 3-6, 6-3, 7-6 (7/2).