Porsche Grand Prix, Filderstadt
Kim Clijsters insists Serena Williams is the true world number one, despite the Belgian having held top spot since early August.
Clijsters is expected to take on Daniela Hantuchova in the first round on Wednesday despite a recent ankle injury.
And although she could lose her number one ranking to compatriot Justine Henin-Hardenne this week, Clijsters believes the younger Williams sister is the best player in the world.
"If she was injury-free she's the toughest to beat out there," said Clijsters. "If Serena played the number of tournaments that I play I definitely think that she would be number one."
And Clijsters again dismissed suggestions that she and Henin-Hardenne do not get on.
"We're colleagues and friends, a combination, and it doesn't matter if we're playing against each other," said Clijsters.
We play to win, but then we get back in the locker room after the match and we're talking. That's what it should be all about. We're rivals on the court, but you can be friends too."
Italy's Silvia Farina Elia edged South Arican Amanda Coetzer 7-6 7-6 to reach the second round in Filderstadt.
In the only other first-round match on the opening day, Spain's Conchita Martinez ousted the only German player in the main draw, wild card Anna-Lena Groenefeld, 7-6 6-2.
The opening day's play in Tashkent was postponed because of persistent rain.
Fifth seed Flavia Pennetta of Italy, sixth seed Jill Craybas of the United States, and eighth seed Jelena Kostanic of Croatia will now open their campaigns on Tuesday.
Top seed Petra Mandula of Hungary, ranked number 41 in the world, will play wildcard Akgul Amanmuradova of