By Scott Malone

RIO DE JANEIRO (Reuters) - American Ashton Eaton won his second straight Olympic decathlon gold medal on Thursday, extending his reign in a sport whose champion earns the title of the world's greatest athlete.

Eaton edged France's Kevin Mayer, who had threatened his position with strong showings in the pole vault and javelin throw, into the silver medal position.

The twice world champion became just the third man to win the Olympic decathlon twice, a feat last achieved by Briton Daley Thompson at the 1984 Los Angeles Games.

"To win two Olympic golds in a row like Daley Thompson is very special. One day, I'm going to have to meet Daley, shake his hand and thank him for giving me something to chase after," Eaton told reporters after tearfully embracing his Canadian wife Brianne Theisen-Eaton who won the bronze medal in the women's heptathlon.

His coach, Harry Marra, said Eaton's performance was all the more impressive given that he had thrown poorly in the javelin as a result of a sore shoulder from the pole vault.

"There's a lot of good athletes but sometimes when you go in the tank on an event, the rest of the whole meet goes in the tank. They don't, they just keep fighting back," Marra said, referring to Eaton and Theisen-Eaton, who he also coaches.

"Repeating a decathlon (gold), repeating when so many things can go wrong, that's impressive," Marra added. "It's historic."

Eaton, whose performance fell short of the world record he set last year in Beijing, said he had worked to improve his throwing events.

"My throwing has been bad in the past, but I really got after the discus and shot here," Eaton said.

"Can I do three in a row? Maybe you should ask Daley,"

Canadian Damian Warner, who beat the 28-year-old Eaton in the 100m with an Olympic best time of 10.3 seconds as well as in the 110m hurdles, snagged the bronze.

"I came here with mindset of gold but there are a lot of tough competitors out there in decathlon," Warner said. "I am proud of myself. I feel like the luckiest athlete in the world."

Eaton won two of the 10 events - the long jump and 400m - and finished second to Warner in the 100m and 110m hurdles.

His final score of 8,893 points tied the Olympic record set in 2004 by Roman Sebrle of the Czech Republic.

(Editing by Ed Osmond)