The deepest field of professional triathletes in North America this year -- a doubling in prize money helps -- promises to make Sunday's running of the Avia Vineman 70.3 triathlon as competitive as ever.

Coursing through wine country after a Russian River swim, the Vineman long has drawn large fields of professional and age-group athletes alike. The 21st annual edition sold out its 2,300 entries in a record five days.

"It's always been a big race, a popular race and a competitive event. The depth of the field is pretty amazing this year," said Vineman spokesman Dave Latourette.

The Vineman -- a 1.2- mile swim, 56-mile bike ride and 13.1-mile run -- starts at 6:30 a.m. Sunday at Johnson's Beach in Guerneville. Top racers finish around four hours later.

The professionals are competing for $50,000 in prize money and points that add up in rankings for the Ford Ironman and Ironman 70.3 World Championships.

Two-time and defending Vineman winner Chris Lieto, course record holder Joe Gambles, and last year's second-place finisher Kieran Doe head the men's field. Also racing is Andy Potts, winner of five races this year.

Back in the women's race are Ironman world champion and defending Vineman 70.3 champion Mirinda Carfrae and Leanda Cave, who finished in second to Carfrae at the Vineman last year.

Vineman Inc., the nonprofit putting on the race, doubled the prize money to attract a deep field of 55 professional triathletes.

Vineman's place on the racing calendar the middle of July also makes the event a great tune-up for the Ironman 70.3 World Championships on Sept. 11 in Las Vegas.

"The timing in relation to the Ironman World Championships is pretty good for guys trying to get ready for that race," Latourette said.

The rest of the field filled up quickly because Vineman is a destination race compared with other competitions that draw more regional entries.

Following the swim, Vineman features a bike ride through the heart of Sonoma County's wine country and a run around Windsor's rural reaches that begins and ends at Windsor High.

Sunday's race is half the distance of the Full Vineman Triathlon, which is set for July 30. So popular are the races they were split in 2000 to give more triathletes a chance to compete.

Hundreds of volunteers are posted throughout the event, particularly at turns and aid stations.

The field is divided into groups for the beginning of the swim for staggered starts. Runners are still on the course into the afternoon.

Conditions should be very good. Water temperatures are expected to be in the mid-70s. The weather forecast calls for the typical morning patchy fog with afternoon high temperatures near 77.