Spencer's long-time coach Charlie Stewart from the Windsor Boxing Club has been brought to London even though he isn't an official team coach.
"It wouldn't be the same if he wasn't here,'' Spencer, 27, told the Toronto Sun. "He's been there with me for 10 years. How could I not have Charlie here?
[Slideshow: Women's boxing makes Olympic debut]
"Just the comfort of having him around, because when I'm nervous I want someone who's familiar around. I take what he says to heart. He's an amazing coach. He's a master at strategy. He can pick apart fighters. He can find their weaknesses. He knows what to do to exploit them."
Funding from Own the Podium helped pay to have Stewart flown to London. Boxing team officials also had Stewart attend pre-Olympic training in Belfast, Northern Ireland. Team massage therapist Ricardo Santia has been working on the veteran trainer's sore hips and back so he can work the corner with coach Sylvan Gagnon for Spencer's fights.
Spencer, a three-time world champion, meets Li Jinzi of China in her first bout. A win puts her in the medal round.
Li was the 75-kilogram world champion in 2008. Spencer won the world title in the 69-kilogram group that year. Spencer defeated Li 14-2 in the final at the 2010 worlds.
Daniel Trepanier, Boxing Canada's high performance director, said no one is taking Li lightly.
"We know it's not the same girl," she said. ''The Chinese put a lot of money on their program for boxing and she's way better than she was for 2010.
''But it's been a long time since I've seen Mary in this condition. I think not going into the Olympic as the No.1, she's more angry than ever to take her place back at the top."
Spencer was the focus of a lot of attention leading up to the Olympics but Canada's two male boxers have packed a punch of their own at the Games.
Simon Kean, a super heavyweight from Tois-Rivieres, Que., defeated Tony Yoka of France last week and faces Kazakhstan bruiser Ivan Dychko Monday.
Welterweight Custio Clayton of Dartmouth, N.S., who has already won two bouts and now faces European champion Freddie Evans Tuesday in the quarter-finals. If Clayton defeats the Welshman, he's guaranteed a medal.
The last time Canada won a medal at the Games was 1996. Canada had not even won an Olympic bout since 2004 in Athens.
Spencer almost didn't get to fight in London. She lost her opening bout against Sweden's Anna Rosalie Laurell at the women's world boxing championships in China. Two automatic Olympic spots were available to be won by boxers from the Americas at the championships.
The Wiarton, Ont., native finally had her ticket to London punched when the International Olympic Committee's Tripartite Commission decided to give her the lone wild card berth in the 75-kilogram class.
Stewart hurt his hip years ago and could hardly walk at one time. He's happy to be able to work Spencer's corner even if he's unable to climb up into the ring.
''I feel a lot better," Stewart said. "I know Mary wants me in the ring. So I have to do what I can to be there."
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