Thomas Muster suffered a surprise second-round defeat in the Newsweek Champions Cup in Indian Wells, California, yesterday - just 48 hours after regaining his world No 1 ranking.
Muster, who was seeded second and had a first-round bye, was beaten 6- 3, 7-5 by Romania's Adrian Voinea.
This is the second time that Muster, fresh from victory on clay in Mexico City, has risen to No 1 only to lose his next match. In February he was beaten in Dubai by Australia's Sandon Stolle, and this latest setback means he has still to taste victory while top of the rankings, although he can still hold onto the position if Andre Agassi and Pete Sampras lose promptly.
In Copenhagen, Britain's Tim Henman, who is unseeded, continued his recent success by beating Germany's Marc Goellner, seeded eighth, 6-3, 6-3 to reach the quarter-finals of the ATP event. Henman now faces another German, Martin Sinner.
Henman, ranked No 64 in the world, reached the semi-finals of Rotterdam's ATP tournament last week before losing to Russia's Yevgeny Kafelnikov.