Top seed Caroline Wozniacki emerged from a testing first set to defeat Monica Niculescu 7-5 6-1 and reach the quarter-finals of the Qatar Open.

The Australian Open champion did not always have it her own way on centre court in Doha, but she eventually found her rhythm to win in straight sets in front of the watching world number two Simona Halep.

The unseeded Niculescu had beaten Maria Sharapova - later revealed to be injured - and seen Magdalena Rybarikova retire to reach this stage, but the Romanian could not keep that up against Wozniacki.

Halep's win earlier in the day had put added pressure on the world number one, who would have fallen in the rankings with defeat, and Wozniacki stumbled from 4-1 up, losing four straight games amid rows with the umpire over her opponent's grunting.

The Dane managed to regain her composure, however, breaking Niculescu as she served for the set and winning the next two games to move ahead.

Wozniacki took complete control from that point onwards and her trials were quickly forgotten as she moved 3-0 ahead in the second set, this time offering her opponent no route back into the match.

Victory was wrapped up inside an hour and a half as Niculescu's challenge faded.