Spaniard Francisco Mancebo took the Tour of California lead on Sunday with victory in the first stage on a rain-soaked day when Lance Armstrong had his time-trial bike stolen.
The 37-year-old Armstrong, who is competing in North America for the first time since his return from retirement, finished the 173.2 kilometre Davis to Santa Rosa stage in a chasing group about two minutes off the pace.
His time trial bike, valued at more than $10,000, was taken from a team truck in Sacramento where Armstrong had used it in Saturday's prologue. Road bikes belonging to three of his team mates were also taken.
Despite the loss, Armstrong said he thought he would be able to catch up with the leaders later in the nine-day tour.
"It was a tough day and we had to chase earlier than we planned but I'm confident I can take time back in the time trial," said the seven-times Tour de France winner, who trails Mancebo by one minute and five seconds.
With his win, Mancebo moved from 40th position into a 1:02 lead over two-times defending race titlist Levi Leipheimer of the U.S. with David Zabriskie third overall, trailing by 1:03.
Mancebo went to the front within a few kilometres of the start Sunday and rode alone for much of the day before finishing in 4 hours 11 minutes 7 seconds.
Jurgen Van de Walle of Belgium was second, with Italian Vincenzo Nibali third.
Fabian Cancellara of Switzerland, who held a two-second race lead after capturing the prologue on Saturday, withdrew because of a virus after 67 kilometres.
The race continues Monday with the 186.6-kilometre second stage from Sausalito to Santa Cruz.