The 22-year-old from London, Ont., who was playing high school basketball just a few years ago, finished fifth in the decathlon Thursday at the London Olympics.
The result was a monumental leap forward from 18th at last year's world championship. His score of 8,442 points ranks second in Canada only to Michael Smith's 8,626.
Warner's result was the best for a Canadian in the Olympics since Dave Steen won a bronze medal in 1988 with a score of 8,328. Warner posted six personal bests over the 10 events.
"I knew I was capable of putting up these scores," Warner said. "Thankfully for me now I put them up in this competition when it really mattered.
"It was a big goal just to make it to the Olympics and come here to put together my best score. I couldn't ask for anything more."
The U.S. finished one-two with Ashton Eaton (8,869 points) and Trey Hardee (8,671 points) claiming gold and silver. Leonel Suarez (8,523) of Cuba won bronze for the second straight Games.
Warner emerged from the opening day's 100 metres, long jump, shot put, high jump and 400 metres ranked third. He clipped a hurdle Thursday morning, had his weakest event — discus — and then struggled in pole vault to slip to fourth.
Still one spot off the podium after javelin, Warner ran the fastest 1,500 metres of his life. It was a tall order to overtake the more experienced Suarez, however, and Warner was passed by Han Van Alphen of Belgium.
"Obviously I was confident in my abilities, but coming into this competition, I didn't set any numbers goal," Warner said. "I'm a numbers guys and I usually do.
"This time I said I was just going to come here, enjoy my experience, have fun and that's what I did and the numbers came like I thought they did. I learned so much about myself here and just about how I compete."
He was playing basketball at Montcalm Secondary School when coaches Gar Leyshon and Dennis Nielson approached him about trying track and field. Warner didn't compete in his first decathlon at the national championships until two years ago.
Warner was nervous at last year's world championship in Daegu, South Korea, competing against Eaton and Hardee, but said he wasn't here in London.
Les Gramantik, who coached Smith, oversaw Warner's progress as the Canadian team's coach of field events in London.
"It was a hell of a score," Gramantik said. "I could almost say a star was born.
"Damian has incredible abilities. His speed is superior. He doesn't have the size but most of the current decathletes aren't big monsters anymore."
"He's a calm, even-keeled guy. He doesn't seem to get too up or down, which is an important thing in decathlon. It's like playing goalie in hockey or a quarterback. If somebody beats you once and you're flustered, it's over. You've got to take it and move on."
Jessica Smith of North Vancouver, B.C., was seventh in her semifinal heat and didn't advance in the women's 800 metres. Vancouver's Elizabeth Gleadle finished 12th in women's javelin.