World number two Justine Henin battled past fifth seed Patty Schnyder 3-6 6-4 7-5 to set up a Qatar Open semi-final against Jelena Jankovic of Serbia.
Henin won last week's Dubai Open crown
Belgium's Henin saved a match point in the third set at 4-5 and 30-40 down, and a lucky net cord and a service break in the 12th game sealed victory.
Daniela Hantuchova fought back from a set and a break down to beat third seed Martina Hingis 1-6 6-4 6-4.
The Slovakian now plays Russia's Svetlana Kuznetsova.
In my mind I always thought I had a chance, even when I was 1-4 down after losing the first set
The second seed breezed past Francesca Schiavone of Italy 6-3 6-4, while fourth seed Jankovic beat Ukrainian Kateryna Bondarenko 6-3 6-3.
Henin, who won last week's Dubai Open, said: "It was a tough match but I had predicted it.
"We are always involved in big fights, in three sets. She is a special player as she is a left-hander."
Hantuchova seemed headed for a quick exit as she surrendered the first set and quickly fell 4-1 down in the next.
But she won seven straight games to claim the set and take the advantage in the decider as she went on to victory.
"In my mind I always thought I had a chance, even when I was 1-4 down after losing the first set 1-6," said Hantuchova.
"With Martina missing lots of balls I knew it was (only) a matter of time.
"I am proud of the way I turned the match around.
"I just stayed positive and played my game and beat a top-10 player. I am happy about it."