The 17-year-old Russian, ranked 12th in the world, double-faulted 20 times in a surprise defeat to Silvia Farina, the Italian well below her in the world rankings, in the Kremlin Cup. She left the Centre Court of the Olympiisky Sports Complex in Moscow to the angry whistles of the crowd after disappointing her fans with an array of unforced errors, double- faults and apparent lack of effort.
Kournikova, seeded No 6, dropped the first set, 7-6. She recovered to take the second set 6-4 and level the match, but lost her composure and succumbed without a fight, losing the deciding set 1-6.
It was Kournikova's first defeat since early last year to a player ranked outside the world's top 15, though her form has been on the slide recently. A week ago in Zurich, she served 17 double-faults to lose in the first round of the European Championships.
Kournikova, who now lives and trains in Florida, dropped out of the top 10 after tearing ligaments in her right thumb.
The teenager was not the only seeded player to lose yesterday. Chanda Rubin, of the United States, defeated the eighth-seeded Romanian, Irina Spirlea, in straight sets, 6-2, 6-3.
In other matches in Moscow, the Belgian left-hander, Sabine Appelmans beat Elena Dementieva 6-4, 6-4, while the fifth-seeded Mary Pierce beat last year's Kremlin Cup runner-up, Ai Sugiyama, 5-7, 6-2, 6-4. Sandrine Testud, seeded No 7, beat her French compatriot, Nathalie Dechy, 6-2, 6-2.
Goran Ivanisevic was another highly ranked player to fall yesterday. The Croatian was one set up against the Slovakian, Jan Kroslak, in the Czech Indoor Tournament in Ostrava, but slumped in the next and lost the third-set tie-break to complete a 4-6, 6-2, 7-6 victory for Kroslak.
Mark Philippoussis was also less than happy in Ostrava yesterday. The sixth-seeded Australian lost 6-3, 6-7, 6-3 to the German player, David Prinosil in the Czech Indoor.
Andre Agassi, though, was one notable name who could be content with his day's work yesterday. The resurgent American beat Kent Carlsen, of Denmark, 6-4, 6-4.