BY THE TIME he made the transition from bike to run at last June's Boise half-Ironman, Chris Lieto owned a new cycling-course record and a five-minute lead on Australian Craig Alexander, the sport's reigning world champion. Good stuff. Except that, for Lieto, big time gaps and course records often become heartbreaking footnotes once he pulls on his running shoes. Indeed, in the final 100 yards of Boise's 13.1-mile run, Alexander caught Lieto, then outkicked him to the finish by two seconds. Lieto collapsed on the asphalt, his arms covering his face. To hear him describe it now, this was progress. "I learned a lot from Boise," says the 37-year-old from Danville, California. "Craig said it was one of the hardest runs he'd ever had."

That kind of sunny disposition will come in handy when Lieto arrives in Kona, Hawaii, for the October 10 Ironman World Championships, an event that's desperately in need of some Yankee mojo. Since legends Mark Allen and Dave Scott retired their aerobars in the mid-nineties, triathlon's signature showcase has lost its coveted position in that limited space Americans reserve for sports without sidelines. Cycling (thanks, Lance) and swimming (thanks, Michael) have long since taken its place. And while triathlon is experiencing unprecedented growth among participants—USA Triathlon now boasts 115,000 members, nearly six times as many as in 2000—no American has placed at Kona since Tim DeBoom claimed back-to-back titles in 2001 and 2002. Lieto could break the drought and help return his sport to popular favor.

A former water-polo player at Long Beach State, Lieto started racing triathlons in 1998, at 25. "When I decided to get into triathlon," he says of his late start, "I didn't own running shoes and I didn't own a bike." Benefiting from a lean six-foot frame and an unusually high power-to-weight ratio on the pedals, he quickly climbed the amateur ranks, making a name for himself on the bike. He turned pro in 2001 and has since broken a dozen cycling-course records and collected a major win at the 2005 Ironman Canada. But in Kona, where he finished a career-best sixth in 2007, he's never been able to hold on to a lead. "He's the best pure cyclist in the race," says Brad Culp, editor of Triathlete magazine. "But to win, he's got to have a huge, 10-to-15-minute gap. He's never going to win Kona on the run, and I think he knows that."

Lieto agrees—mostly. He thinks seven minutes is all he needs and says he'll never change his hammering style to "save himself for the run."

"It's much more difficult to be in the lead," he concedes. "You don't know what's happening behind you. But my greatest strength is my cycling ability, and I plan to take advantage of that."