Second seed Lindsay Davenport reached the semi-finals of the Swisscom Challenge in Zurich with a straight sets win over Kim Clijsters.

Davenport, who has missed much of the season through injury, was too strong for the Belgian sixth seed and emerged a 6-3 7-6 (7-5) winner.

The American broke early in then sealed the first set with another break.

Clijsters looked vulnerable throughout the second set and had to save a matchpoint at 4-5.

She then earned two break points in the next game but could not convert them and the match went into a tie-break.

Davenport raced to a 6-1 lead but then squandered four match points before clinching victory.

Davenport's next opponent will be Justine Henin, the Belgian fourth seed who defeated Marie-Gaianeh Mikaelian of Switzerland, 7-5, 6-2.

Veteran Conchita Martinez beat American qualifier Alexandra Stevenson 7-5 7-5 to book a place in the last four.

Stevenson, who came through a gruelling three-setter against fifth seed Jelena Dokic on Thursday, looked tired and was often caught flat-footed.

Stevenson broke first for a 5-4 lead but immediately ceded her advantage and Martinez then broke again, securing the set with a forehand winner down the line.

The 21-year-old American looked less sluggish in the second set but handed the match to her 30-year-old opponent when she hit a smash wide at 5-6 down.

Former Wimbledon champion Martinez is enjoying a good week, having beaten top seed Jennifer Capriati in the previous round.

Martinez will next take on Patty Schnyder, who beat Daniela Hantuchova 6-7 6-3 7-6 on Friday.

In a long and dramatic contest that lasted for two hours and 42 minutes, Schnyder recovered from losing the first set to outlast and ultimately out-power her seventh-seeded teenage opponent.