Justine Henin-Hardenne and Kim Clijsters struggled into the Ordina Open semi-finals on Thursday, moving a step closer to another Belgian showdown.

Second seed Henin-Hardenne, who beat Clijsters in the French Open final 12 days ago, struggled to a 3-6 7-5 6-3 victory over Slovakian Ludmila Cervanova, while top-seeded Clijsters battled to a 7-6 7-6 win over Slovenian Tina Pisnik.

With Wimbledon just four days away, both players have work to do if they are to repeat their French Open feat.

Cervanova, the world number 87, deservedly won the first set against Henin-Hardenne thanks to her powerful groundstrokes.

When she broke in the opening game of the second set, an upset looked possible, but Henin-Hardenne battled back to lead 4-2 and eventually stole the set.

Henin-Hardenne then broke to lead 2-0 in the decider and maintained her momentum to take victory.

"At first I was not aggressive enough," Henin-Hardenne said. "She played really well and I had to continue to keep fighting which I did, and I won."

Clijsters, chasing her first title on grass, was pushed hard by Pisnik, a good serve and volleyer, who beat her at the same stage last year.

"The problem today was that I couldn't really play my game," Clijsters said. "She makes it really tough with her slice because you can't really attack the ball.

"But I was really motivated today to get my revenge after she beat me last year."

Clijsters served for the match at 5-3 in the second set, but Pisnik broke back.

ANOTHER TIEBREAK

The Slovenian held for 5-5 and broke again to serve for the second set, only to be broken to 15 as the match went to a another tiebreak.

This time, Clijsters' greater consistency was the key and she clinched her place in the last four when Pisnik netted an easy volley.

Fifth seed Nadia Petrova, a French Open semi-finalist, beat compatriot and fourth seed Elena Dementieva 6-4 3-6 6-2 to set up a meeting with Henin-Hardenne.

German Barbara Rittner followed up her victory over Amelie Mauresmo by thrashing sixth seed Iroda Tulyaganova of Uzbekistan 6-2 6-1.

She will play Clijsters in the last four.

The men's event was overshadowed by Richard Krajicek's retirement due to his continuing fitness problems.

The elbow injury that forced him to withdraw from Wimbledon this week was the last straw for the Dutchman, who will be remembered most for winning Wimbledon in 1996.

Dutch qualifier Dennis van Scheppingen did his best to lift the crowd but went down in three sets to seventh seed Arnaud Clement, the Frenchman winning 7-6 6-7 6-3.

He will play Fernando Vicente in the quarter-finals after the Spaniard rallied to beat German Lars Burgsmueller 4-6 6-4 6-4.

Top seed Jiri Novak cruised into the last eight with a 6-2 6-4 win over Krajicek's conqueror Olivier Mutis.

Novak will meet Jan Vacek in the quarter-finals after the Czech upset fifth seed Sebastien Grosjean, last week's Stella Artois finalist, 6-4 3-6 6-2.