Kim Clijsters got her Antwerp Diamond Games bid off to a solid start on Wednesday, brushing aside Spain's Aranxta Parra 6-3, 6-2 to reach the last eight.
But former French and Australian Open champion Mary Pierce, who lost to the Belgian world number two in Sunday's Paris Open final, was beaten 6-4, 6-4 by ninth-seeded Magdalena Maleeva.
Second-seeded Clijsters, given a bye in round one, clinched victory on her third match point and was full of praise for her opponent, who got through to the second round as a qualifier.
"She is Spanish but does not play like your usual Spanish player... she has a great serve and is very aggressive," said Clijsters. "To win against her was not easy, believe me".
Instead of conserving her energy, Clijsters will play with younger sister Elke in the doubles on Thursday.
"I think next year I will not play doubles at all but right now I'm enjoying myself enormously and I always give 100 percent. It's great to be here. As a matter of fact, I have more fun here than in the Grand Slam tournaments."
Clijsters' compatriot, top seed and world number one Justine Henin-Hardenne, begins her campaign on Thursday after being given a late start to help her recover from a throat infection. She will take on Czech Denisa Chladkova in the second round.
TENSE MALEEVA
Bulgarian Maleeva had to fight hard to get past Frenchwoman Pierce, who has been in top form and whose path to Sunday's Paris final took her up 10 places in the world rankings to 27th.
"Mary played well and I was tense during the whole match," said Maleeva. "I really had to clench my teeth to finish the second set because Mary was getting better and better," added the Bulgarian, who has taken a liking to the Diamond Games.
"They (the huge crowd) help us to play well, for sure. But there is another reason why I like this tournament very much. It was the first event I played in 1999 after having surgery on my serving shoulder and all went well".
Maleeva will now meet Czech Iveta Benesova, who beat Eleni Daniilidou of Greece 7-5, 6-4 earlier on Wednesday, with the winner facing Clijsters in the quarter-finals.
Two qualifiers are also through to the last eight after Czech Klara Koukalova beat Russian Dinara Safina 6-4, 7-6 and Croatian Karolina Sprem got past Zimbabwe's Cara Black 6-4, 6-3.
Belgian doubles specialist Els Callens took the first set from eighth-seeded Silvia Farina Elia but eventually lost 3-6, 6-2, 6-1 to the Italian, who moves into the last eight.
Ukraine's Julia Vakulenko thrashed Alexandra Stevenson of the United States 6-3, 6-1 in their first-round match.
