DUBAI - Caroline Wozniacki overcame a persistent fever, a seed-beater, difficulties with her first serve, and a late night finish to reach the semi-finals of the Dubai Open for the fifth successive time on Thursday.

The former world number one from Denmark's 7-5, 6-0 win over the world number 14 from Italy, Flavia Pennetta, confirmed the feeling that she is gradually edging her way back towards the summit, even though her standard was not always all she wanted. Wozbiacki twice conceded early breaks of serve before repairing the damage, and was unable to force her advantage home when she was twice within two points of taking the first set.

She nevertheless struck her ground strokes consistently, if not always as forcibly as she has recently. Once she had a set in the bag Wozniacki accelerated her progress encouragingly against an opponent who had dismissed the seventh-seeded Angelique Kerber the previous day. "Obviously with the way I have been feeling this week, I'm just trying to save as much energy as I can for all the matches I have to play," Wozniacki said.

"I'm definitely very pleased with the way I have played and the way I fought. Even when I haven't felt good, I've still managed to win. "But today, you know, with the fever down, I definitely felt much better. Hopefully it's a step in the right direction, and I don't mind being sick for the rest of this week because obviously that's bringing me some good luck." Wozniacki next plays the top seed, Simona Halep, who had a much closer call to reach the semis.

The lively and creative Romanian was within one point of going a break down in the seventh game of the final set before surviving 6-3, 1-6, 7-5 against Ekaterina Makarova, a deceptive left-hander from Russia. Halep then led 5-3, was broken to love, reached 6-5 and still needed five match points before she was able to close it out.

The other semi-final will be between two of the newest and most interesting young climbers in the world's top 30, Karolina Pliskova and Garbine Muguruza. Pliskova, a striking 22-year-old from Prague, upset the seedings for the second successive day and reached the semi-finals for the second successive week.

She also turned her match dramatically on its head from a set and 1-3 down in a 3-6, 7-6(7-5), 6-1 win over Lucie Safarova, her 11th seeded compatriot. Last week the tall Czech with one of the steepest and most dangerous first serves in the game reached the Antwerp semis, and last month she became the youngest top 20 player by breaking into the top echelon for the first time.

However, she had to survive a crisis at 5-5 in the second set when she slipped to 15-40, within one solid blow of probable defeat, before altering the psychology of the match utterly in an emotion-turning last point of the tie-break. Muguruza, a 21-year-old from Barcelona, delivered a 6-7(4-7), 6-3, 6-3 win over her doubles partner Carla Suarez Navarro, the 13th seed who had eliminated the Wimbledon champion, Petra Kvitova.

Navarro, with her great movement and battling ground strokes, tenaciously saved three set points and grabbed the first set, but Muguruza, calm and elegantly proficient in all areas thereafter looked slightly the more likely to win a high quality encounter full of fluent rallies, Muguruza said she was helped by her coach Alejo Macisidor.