Sydor, 30, a mountain bike silver medalist at the Atlanta Olympics, shot from the starter's ramp and proceeded to pedal over the obstacle-strewn, three-mile course in a women's record six minutes, 44.96 seconds.
California's Shari Kain finished second to Sydor among pro cross country women in 6:59.14, followed by Canada's Chrissy Redden in 7:00.55. Spain's Maria Steb topped the women's down-hill division in 7:30.82.
Norway's Rune Hoydahl posted the fastest time among cross country pro men, covering the same challenging course in 6:04.35. Sweden's Roger Persson placed second in 6:04.42, followed by Switzerland's Beat Wabel in 6:05.86. Australia's Michael Ronning led the men's pro down hill cyclists in 6:05.56.
Yesterday's second event of the five-day Outrigger Hotels Hawaiian Mountain Tour drew 140 professional riders, mostly from North America and Europe. Nearly all of the 200 competing amateurs hail from Hawaii.
The racers were sent off at 30-second intervals.
The high-tech cycles run from $1,000 basic bikes to fully-suspended models costing $4,000 or more.
"This course was not that technically demanding. But it did require strong leg power," said Sydor, a three-time world mountain bike champion.
The race was a sprint -- short, fast with obstacles adding to the challenge. "A good test of one's physical fitness," Sydor said.
In addition to elements, riders were challenged by numerous sharp turns on slick grass; dodging water hazards and riding up a flight of rock stairs.
"We threw the works at the riders but they came through," said race director Dave Nicholas of organizing Event Marketing Inc.
"A pretty easy course -- kind of a showcase for Honolulu fans," said Steve Delacruz, a former Hawaii biking champ now living in California. The former Punahou School athlete finished 39th among the pro men.
While visitors swept the men's and women's professional cross country and down hill races, local riders dominated the amateur divisions.
"We've made mountain bike racing a family sport," said the Big Island's Tom McCarthy, who, along with son Garuda, 18, and daughter Tulsi, 17, competed yesterday.
Tom, 47, topped the beginning men's master division; Garuda placed 42nd among pro cross country men, and Tulsi finished first among junior amateur girls.
Brent Imonen, 28, Hawaii's best triathlete, is giving pro mountain biking a try.
"Triathlons will always be my first sport," he said. "but learning pro mountain biking sounds like a challenge. I hope I'm up for it." Imonen finished 44th among cross country men's pros.
Honolulu's Ray Brust topped the expert senior men's division in 6:47:66. "A windy, slippery and fast course but I felt pretty confident out there. I look forward to a good tour," he said.
The $50,000 Hawaiian Mountain Tour runs through Sunday, with down hill, cross country, slaloms and criterium events scheduled at Windward Oahu's Kualoa Ranch. Racing begins at 8 a.m. each day. Admission is free.