SANTA ROSA, Calif. — Lance Armstrong finished among the leaders in the Tour of California's opening stage on an exasperating Sunday that included drenching rain, a flat tire and even the theft of his time-trial bike.

Armstrong persevered through his profoundly gloomy day to finish near the front of a grueling 107-mile stage. He led a chase group that never quite caught up to the soaked race leaders, including surprise stage winner Francisco Mancebo of Spain.

But the day began inauspiciously and got worse before a solid finish by Armstrong, who might have been rethinking his comeback during five frigid hours in the rain — if he hadn't already endured much tougher struggles with cancer and doping allegations during a historic racing career that includes seven Tour de France titles.

"Holy hell. That was terrible," Armstrong wrote on his Twitter feed about 15 minutes after finishing. "Maybe one of the toughest days I've had on a bike, purely based on the conditions. I'm still freezing."

Cycling doesn't get much more exasperating than it did Sunday for Team Astana, which lost four bikes to thieves Saturday night, some time after Armstrong finished 10th in the prologue. His time-trial bike was stolen from the Astana truck in Sacramento along with the race bikes of teammates Steve Morabito, Yaroslav Popovych and Janez Brajkovic.

Astana spokesman Philippe Maertens confirmed the bike thefts to The Associated Press after it was reported by Armstrong himself on Twitter. Armstrong later posted a picture of his missing bike, which has distinctive yellow-and-black wheels and the logo of his Livestrong foundation.

"There is only one like it in the world therefore hard to pawn it off. Reward being offered," Armstrong wrote.

The rain fell in steady sheets from the opening miles of Stage 1 in Davis, a famously bike-friendly college town southwest of Sacramento. Most riders needed about five difficult hours to cross the rolling hills of the Napa Valley before ending up in Sonoma County, but Armstrong stayed in contention despite a flat tire along the way.

Mancebo, an 11-year pro who joined Rock Racing this year, took an early lead and stayed in front of a chase group that included Levi Leipheimer and Armstrong until the downtown finish, when Vincenzo Nibali of Liquigas caught him with just one lap to go on the three-lap circuit. Mancebo somehow reclaimed the lead and barely held off Nibali and Quickstep's Jurgen Van de Walle in a surprisingly entertaining finish under such awful weather conditions.

The Tour of California is Armstrong's first competitive appearance in his native country since beginning his comeback last month.

Fabian Cancellara, the Swiss Olympic champion who edged Leipheimer to win the prologue, dropped out of the race midway through the opening stage with a fever. Leipheimer, Armstrong's teammate and the two-time defending Tour champion, also felt ill, but the Santa Rosa native stayed in the race.

Armstrong won't need his time-trial bike again until Friday in Solvang, where the race holds its second time trial. That segment is crucial to Astana's hopes of winning the overall team title, however.