By Scott Malone

RIO DE JANEIRO (Reuters) - American defending champion Ashton Eaton and Canadian world record holder Damian Warner kicked off the battle for decathlon gold on Wednesday, with Eaton making up for a second place 100 meters finish with a strong long jump.

Warner set an Olympic best of 10.3 seconds for the decathlon 100m on the event's first day, easily bettering the 10.46 of Eaton, who normally counts on his speed to post high scores.

The 28-year-old Eaton speaks of North American teamwork when the subject turns to his Canadian heptathlete wife and bronze medalist Brianne Theisen-Eaton. That alliance clearly did not apply to Warner, who finished fifth at the 2012 London Games.

Eaton responded to Warner's blazing sprint with a 7.94m long jump, besting Warner's 7.67m, and 14.73m shot put, over Warner's 13.66, to reclaim the lead.

But neither of the leaders were dominant in the shot put or high jump.

American Jeremy Taiwo climbed into third overall thanks to the best high jump performance, clearing 2.19m, just ahead of Belgium's Thomas van der Plaetsen's 2.16.

France's Kevin Mayer led the shot put with a 15.76m throw.

The crowd's clear favorite was Brazil's Luiz Alberto de Araujo, who had climbed into fourth on the strength of a 15.26m shot put but dropped to 12th after only clearing 1.92m in the high jump.

The event continues Wednesday evening with the 400m.

(Reporting by Scott Malone; Editing by Alison Williams)