Third-seeded Agnieszka Radwanska came through a tough first set before beating Monica Niculescu 7-5 6-1 on Wednesday to reach the quarter-finals of the Qatar Open.
Radwanska, who was down a double break in the first set, struggled with her first serves.
But as the match progressed, her superb shot-making gave her Romanian opponent little chance.
Also advancing from the third round was fourth-seeded Garbine Muguruza of Spain, who beat Timea Babos of Hungary 6-2 7-5.
However, fifth-seeded Petra Kvitova of the Czech Republic lost 5-7 6-2 6-1 to Jelena Ostapenko of Latvia.
Kvitova, a two-time Wimbledon champion, came from 3-1 down to win the first set, but Ostapenko continued to play with confidence.
She hit 28 winners before wrapping up the match in one hour and 56 minutes.
