LINZ: Top seeds Flavia Pennetta and Agnieszka Radwanska advanced to the semi-finals of the WTA event in Linz on Friday.

Pennetta was stretched in the opening set of her match with Romania's Ioana Raluca Olaru, but the Italian took control in the second to secure a 7-5, 6-2 victory.

Radwanska fought off two set points against seventh-seeded Czech Lucie Safarova in their second-set tie-break before claiming a 6-3, 7-6 (11/9) victory on her fourth match point.

Third-seeded Belgian Yanina Wickmayer also won, beating eighth seed Sara Errani of Italy 7-5, 6-3, but fourth-seeded Spaniard Carla Suarez Navarro failed to reach the semi-finals, losing 7-5, 6-4 to Czech Petra Kvitova.

Pennetta looked weary in the first set as she struggled to get an upper hand against an opponent who has enjoyed most of her success away from the WTA Tour, winning nine ITF events.

From 3-3, a succession of five consecutive breaks left Pennetta leading 6-5, but she double-faulted on her first set point before closing out the set on her second.

In the second set, Pennetta earned a break for 2-1 but then had to save three break points before holding for a 4-2 lead.

After Olaru had failed to make the most of her opportunity, Pennetta finished strongly by winning 11 of the last 13 points.

"Everyone is tired at the end of the year," said Pennetta.

"Actually I felt a little bit better than yesterday, but she started very aggressive, very focused. She was playing very well today, especially the first set, but then she started having problems with her serve."

Radwanska earned an early break to lead Safarova 3-1, but after breaking again to lead 5-1 she initially failed to serve out the set.

After taking the set at her next opportunity she held three break points at the start of the second set, but Safarova held off the challenge.

Safarova then broke to lead 2-0, but a double-fault allowed Radwanska to break back in the next game.

The Czech left-hander then saved a break point at 2-2 before the set moved to a tie-break, where she was unable to convert two set points at 6-4.

"In the beginning of the match she made a couple of mistakes and I think that's why I was winning very quickly 5-1," said Radwanska.

"But then she played much better and it was very tight. It was like 50-50. For sure I was going to be in trouble in the third set, so I was just trying to be focused on her set points. It was just so close."

There were seven breaks of serve in the first set as Wickmayer tackled Errani, with the Belgian failing to take advantage of three set points on Errani's serve at 5-4 but then breaking her at 6-5.

A break for 2-0 gave her the start she wanted in the second set and although she failed to serve out the match at 5-1 she clinched victory on her fourth match point at 5-3.

Suarez Navarro, who defeated Venus Williams on her way to the 2009 Australian Open quarter-finals, failed to convert any of eight break points she held in the first set, while Kvitova broke at her ninth break-point opportunity to lead 6-5 and serve out for the first set.

In the second set, Kvitova broke to lead 3-2 when Suarez Navarro double-faulted, but she lost her advantage when she double-faulted three times in succession to allow the Spaniard to level at 3-3.

But then, having pulled level, Suarez Navarro dropped her serve again in the next game, and that was enough to give Kvitova a place in the semi-finals.