It turns out he was right.
Warner put up a personal best score of 8,512 points Sunday to finish third in the decathlon and give Canada its first medal of the championships.
Warner was in fourth place after the first day of competition, and mounted a charge to the podium Sunday with personal bests in the pole vault and javelin.
"I said yesterday I wasn't happy with my first day, said I was going to come out swinging today and that's what I did," Warner said. "I stuck with it, I was motivated to get on the podium and I just let that carry me through the events."
Warner moved into medal position in the javelin throw, the ninth event of the decathlon. His throw of 64.67 metres gave him 808 points and moved him ahead of Germany's Rico Freimuth.
He clinched the bronze with a 10th-place finish in the 1,500 metres, giving him a total of 8,512 points over the two-day, 10-discipline event.
It's the first major medal for the native of London, Ont., who placed fifth in the event at the 2012 London Olympics.
Canada's last world championship decathlon medal was by bronze by Michael Smith in 1995.
World-record holder Ashton Eaton of the United States won gold with 8,809 points, while Germany's Michael Schrader was second with 8,670.
Later in the 1,500 metres, Winnipeg's Nicole Sifuentes and Toronto's Kate Van Buskirk advanced to the semifinals of the women's 1,500 metres. And Vancouver's Inaki Gomez placing eight in the men's 20-kilometre race walk.
Warner opened the second day of the decathlon with a time of 13.96 seconds in the 110-metre hurdles to score 980 points.
In the discus he recorded a seasonal best of 44.13 metres to score 749 points, then leaped to a personal best of 4.80 metres in the pole vault for 849 points.
He than made the move into medal territory with his javelin throw and held third place through the 1,500.
"This is such a great feeling, all the hard work my coaches and I put into this the last couple of years," he said. "In 2011 I finished 18th, saw the three medallists running around the track with their country's flags draped over their shoulders, I told my coaches that I want that to be me, pretty special feeling to achieve that."
"I hope this motivates the rest of the team," he added
In the women's 1,500 metres, Sifuentes finished sixth in her preliminary heat in four minutes, 8.54 seconds to qualify automatically for the semifinals. Van Buskirk finished seventh in her heat in 4:08.65, and her time was good enough to go through as one of the six fastest outside the automatic qualifiers.
"All I wanted was to advance, that was my plan," Sifuentes said. "I was a bit out there the whole race, but at least I didn't get boxed in. I knew even if I wasn't top six (to auto-qualify) I would get in on time."
Toronto's Sheila Reid was seventh in her heat and failed to move on.
Gomez finished the race walk with a seasonal-best time of 1:22:21.
"It was tough, it was hot out there," Gomez said. "The pace picked up around 12 kilometres. I tried to stay with the Spanish racer who ended up winning bronze. At 16 kilometres I noticed I had two cards on the board, so I had to be careful from that point. Had to make sure my technique was flawless. I wanted to finish top eight, I accomplished that."
Benjamin Thorne of Kitimat, B.C., was 20th.
Toronto sprinters Gavin Smellie and Aaron Brown ran in the semifinals of the men's 100 metres but failed to qualify.
Brown finished fifth in the semi won by eventual champion Usain Bolt.
"I got out pretty well, obviously Usain's acceleration is crazy," Brown said. "I was running next to him out there. No complaints here, happy with how I performed."