The Belgian edged out Italian Daniel Bennati in a sprint finish, with Oscar Freire of Spain taking third place.

The leading group of riders finished the 154km stage, which began and ended in Baden, in the same time of three hours 51.14 seconds.

Jan Ullrich, who is using the race as part of his Tour de France build-up, was 44th in the same time.

Boonen leads the overall standings because of time bonuses awarded to the first three riders across the line.

It was his 17th victory of the season but his first ever in the Tour of Switzerland. "Now I've won a stage I can relax a bit and enjoy the rest of the race," the Belgian said.

"There are two or maybe three other chances for a sprint finish and so hopefully I can win another stage."

Sunday's second stage, a 165km route from Bremgarten to Einsiedeln, is also likely to favour the sprinters.

The race ends next Sunday with a 30km individual time trial.

Result from stage one of Tour of Switzerland - Baden-Baden (154km)

1. Tom Boonen (Belgium/Quick-Step) 3:51:14"
2. Daniele Bennati (Italy/Lampre) same time
3. Oscar Freire (Spain/Rabobank) same time
4. Alexandre Usov (Belarus/AG2R) same time
5. Allan Davis (Australia/Wuerth) same time
6. Geoffroy Lequatre (France/Cofidis) same time
7. Isaac Galvez (Spain/Caisse d'Epargne) same time
8. Bjoern Schroeder (Germany/Milram) same time
9. Martin Elmiger (Switzerland/Phonak) same time
10. Alexei Markov (Russia/Caisse d'Epargne) same time