GUADALAJARA, Mexico - Amanda Sin put her head down and pedalled furiously 10 minutes up a backbreaking path of rocks and mud, one final climb that propelled the cyclist to Canada's first medal at the Pan American Games.

The 33-year-old from Collingwood, Ont., captured bronze in women's mountain bike Saturday, pulling the pin to open the figurative floodgates of Canada's expected medal haul in Mexico.

Teammate Max Plaxton quickly added a second medal, earning silver in the men's mountain bike, the first events contested at the Games.

Sin powered past teammate Mikaela Kofman on the last of the four 6.2-kilometre loops of the course in Tapalpa, a gut-busting section that was exactly the way she likes it.

"It's very steep with a lot of cobble, rocky, technical and some muddy sections," Sin said. "I really enjoyed it, it was very tough and challenging. That made for a really good race.

"It's really exciting to win the first medal of the Games, so I'm happy to do that for our country."

American Heather Irmiger won the women's gold in one hour 34 minutes nine seconds, while Mexican Laura Lorenza Morfin finished second. Sin was 3:05 back for third while Toronto native Kofman was fourth, 3:59 off the pace.

Colombian Hector Paez finished the five-lap men's course in 1:34.12, pulling away from Plaxton at the top of the final climb to edge the Canadian by 17 seconds. Jeremiah Bishop of the U.S. won the bronze. Derek Zandstra of Trenton, Ont., was eighth.

Canada's first medals were sure to be only the beginning of a continual march to the podium that could average 10 trips a day, based on previous Games. Canada claimed 137 medals four years ago in Rio de Janeiro, Brazil, finishing third behind the U.S. and the host country.

The mountain bike wasn't an Olympic qualifying event -- the two women's and men's spots are chosen based on national ranking and will be determined just a couple of months out from the London Games. As a member of a Canadian women's team ranked No. 1 in the world Sin doesn't face an easy path to London.

Catharine Pendrel, gold medallist at the world championships last month, is among a group of women ranked ahead of her that includes Emily Batty and veteran Marie-Helene Premont.

"It is a goal for sure, but we have the strongest women's team in the world right now," Sin said. "It's very competitive."

Plaxton sat back for most of the course, then made his move on the last lap and had the lead briefly.

"I played what cards I had," he said. "But near the top of the last climb on the last lap, he just accelerated and I had nothing to respond with."

Plaxton's medal capped a strong -- but long -- season that saw him win the Canadian championships and Pro XCT series.

"It's the middle of October, usually my season ends in September," said Plaxton, who chose to compete at the Pan Ams because he'd never been to a multi-sport Games. "It's been a great season, and now with a medal here. . . pretty, pretty happy, but ready for a break for sure."

Both Sin and Paxton marvelled at the crowd that turned out to watch the racing in Tapalpa, a picturesque town that lies in the mountains a 90-minute drive south of Guadalajara. Plaxton, who speaks fluent Spanish after spending four years of his childhood in Chile and four years in Spain, said the crowd rivalled any European World Cup race.

"The fans are awesome. Definitely pushed me," Plaxton said. "And they're everywhere. On the hardest climb they were two, three deep. I was definitely breathing hard because of the altitude, but I coudn't even hear myself breathing they were cheering so loud."

Mountain biking was one of 11 medal events on the first official day of competition at the Games.