Carl Hester has hailed the rise of Charlotte Dujardin but said that he hopes to trump his Great Britain team-mate in the Olympic dressage.
Hester, taking part in his fourth Games, is fifth in the world rankings, with 27-year-old Dujardin one place higher and having set a world record this year.
"I'm amazed by her rise to the top," he told BBC Sport.
"We are competitive with each other and who knows what surprises there may be."
Enfield-born Dujardin came to Hester for lessons in 2007 and has since trained with the 45-year-old.
"The horse (Valegro) she is riding is part-owned by me - questions have been asked whether I kept the right horse," joked Hester, who was raised on Sark in the Channel Islands.
"But Charlotte broke the world and British record this year and that gives me so much pleasure. My horse came out on top last year, but she's worked hard to catch me. I wouldn't be disappointed if she performs better than me at the Olympics.
"It's been a whirlwind rise for her. She rode her first grand prix 18 months ago - it's unbelievable."
Dujardin broke the world record for a Grand Prix special in April before setting a new British freestyle record with a score of 90.65% at the Hartpurey International earlier Festival in July.
She beat the previous mark of 87.6% set by team-mate and current world number two Laura Bechtolsheimer.
"It's great to have Carl," Dujardin told BBC Sport.
"He keeps me very focused and he makes it such fun. He takes the mick out of me, quite a lot. When I'm riding around I wear an earpiece and he says things I don't want to know."
Hester admitted that his sport does not attract a wide audience but said he hoped to "change people's perceptions" at this Games.
"It's obviously a technical sport and not easy to explain to people," said the Barcelona, Sydney and Athens Olympics veteran.
"We need funky music and good composers to get people into it. Charlotte and I use a 26-year-old music guy. The music is fantastic, funky and up to date with real English themes. You can see horses dancing to the music."
Both are in a strong British team, which also features Bechtolsheimer and 56-year-old Richard Davison. The riders stand a great chance on both the team and individual fronts of adding to the team silver won by Britain's eventers. Germany will be their main rivals for gold.
Bechtolsheimer said the rivalry between herself and Dujardin benefited the team.
"We're grateful to be part of this group and hopefully we can get Britain its first Olympic dressage medal," said the 27-year-old, who is the granddaughter of German billionaire Karl-Heinz Kipp.
"It's always good if you have competition in the team. The more that are fighting for the top spot, the better."
Davison, who will compete in the individual dressage competition, is set to compete in his fourth Games, was proud of the progress made by British dressage on the world stage.
"The talent coming through is incredible and we have amazing horses," said the Staffordshire-based rider.
"I've never been to an Olympics with a squad like this. We've won team medals since 1993, but in the last four years world-class horses have been matched with world-class riders and that's when it has really, really kicked in."