Seeded players Elena Vesnina and Peng Shuai reached the quarter-finals of the Pattaya Open with straight sets victories on Thursday.
Fifth seed Vesnina beat Thai wild card Nicha Lertpitaksinchai 6-3 6-3, while Chinese eighth seed Peng overcame Romanian qualifier Alexandra Dulgheru to win 6-3 6-4.
Vesnina struggled to make any impression on Lertpitaksinchai's serve in the early stages as the Thai gave up just one point in her first three service games and held a break point to lead 4-3.
But she sent a forehand wide and then surrendered her own serve in the next game to leave the Russian serving for the set.
In the second set Lertpitaksinchai fought off four break points, broke for 3-1 and held two game points to lead 4-1.
But Vesnina fought off that threat, levelled at 3-3 and went on to win the final 12 points of the match.
"She was serving pretty good today," said Vesnina. "She was changing direction, at the beginning serving flat and then a little more spin.
"(At the end) she kind of dropped her level a little bit and I raised my level up. I stopped doing easy mistakes on my backhand side and I really had two good games on my serve, first serve aces and really good placement."
Peng was stretched by Dulgheru, taking the first set but then allowing her momentum to slip.
The Romanian took charge of the second set to lead 4-1, but Peng staged a gallant comeback to claim the next five games and a place in the last eight.
They were joined in the last eight by veteran Kimiko Date-Krumm who defeated Tadeja Majeric of Slovenia 7-6 6-3.