* Russia, Canada, United States debut in men's hockey
* Home figure skating hero Plushenko pulls out
* Skiers wear sleeveless tops as temperatures rise
* Organisers say relaxed about snow conditions
* Anti-corruption activist criticises Games
By Mike Collett-White
SOCHI, Russia, Feb 13 (Reuters) - Ice hockey mania swept the Winter Olympics on Thursday as the heavyweight men's teams Canada, the United States and hosts Russia played their opening round games in a competition generating more excitement than any other in Sochi.
Underlining the sport's popularity in Russia, and how dearly the home nation would love to win the final held on the last day of the Games, over 10,000 flag-waving fans roared on the men in red to a 5-2 win over Slovenia at the gleaming Bolshoy Ice Dome.
The United States, silver medallists at the Vancouver Games four years ago, laid down a marker by thumping Slovakia 7-1, and defending champions Canada open the defence of their Olympic title against Norway in the day's late match.
But at another venue in Sochi's Olympic park a few hundred metres away, the news was not so happy for the home fans.
Russia's Yevgeny Plushenko, figure skating's ultimate showman who helped the hosts to gold in the team event on Sunday, pulled out of the men's individual event just seconds before he was to start his short programme.
Away from the drama, athletes contested six Olympic titles on the sixth full day of competition at the Feb. 7-23 Games.
In the Caucasus mountains, high above the action in the resort town of Sochi, Joss Christensen of the United States won the inaugural men's freestyle skiing slopestyle.
Gus Kenworthy took silver and Nick Goepper the bronze in a U.S. podium sweep, taking pressure off a team that some domestic media had begun to question as it languished well down the medals leaderboard.
"I am shocked. I am stoked to be up here with my friends. America, we did it!" said Christensen, after another bumper crowd at the Extreme Park saw the skiers push their acrobatic routines to the limits.
In the women's cross-country 10km classic, several athletes wore sleeveless tops as temperatures touched 13C in bright sunshine and contestants complained of tough conditions.
Poland's Justyna Kowalczyk powered to victory, but Russian Natalia Zhukova, who finished seventh, told reporters: "It's the first time of my life that I race in such warm weather."
In the latest weather-related disruption, practice for the men's freestyle skiing aerials event was cancelled because of unseasonably high temperatures.
But organisers played down concerns about the quality of the snow that many athletes have described as slushy and difficult, and which may explain some of the crashes in disciplines ranging from slopestyle to cross country.
"It is a constant battle for winter sports," said Mark Adams, International Olympic Committee spokesman. "We are relaxed but we watch the situation."
Also in the mountains, France's Martin Fourcade won the men's biathlon 20km individual gold medal.
Back in Sochi, Li Jianrou avoided an early pile-up to win the women's 500 metres short track speed skating, extending China's winning streak at the distance to a fourth Winter Games.
The 27-year-old first-time Olympian described it as "a miracle".
Compatriot Zhang Hong claimed the women's 1,000m speed skating title at the Adler Arena, beating pre-race favourites Heather Richardson and Brittany Bowe of the United States.
In the sliding disciplines, a track worker was struck by a bobsleigh and suffered two broken legs, IOC President Thomas Bach told Reuters.
In the last event of the day, the inaugural team relay looks destined to be won by luge powerhouse Germany.
Germany are already top of the medals table with six golds, ahead of Canada, the Netherlands, Norway and the United States on four. Russia are seventh with two.
DREAMING OF HOCKEY GOLD
For Russian President Vladimir Putin, who has staked his legacy on holding a successful Games, the ultimate sporting dream would be the men's ice hockey gold.
Before that can happen, Russia meets the United States on Saturday in a contest that is sure to stir memories of the "Miracle on Ice" at the 1980 Lake Placid Winter Games.
Thirty-four years ago, a group of American college players beat the then Soviet Union's "Big Red Machine" 4-3 in a mismatch of David and Goliath proportions.
The Cold War climate that then prevailed may have thawed, but Putin has conjured the frosty relations of the time to describe Western criticism of his human rights record, and allegations of corruption connected with the Games, which have marred the buildup.
Putin has dismissed charges of widespread corruption, which were levelled at organisers and politicians after the estimated costs reached $51 billion, making them the most expensive Olympics ever held.
Officials dispute the figure, and say that many of the huge construction projects associated with Sochi will help turn the area into an international sports centre of the future.
They hope one of the main lasting legacies will be a Formula One racetrack being laid in and around the Olympic park, which is scheduled to be ready for Russia's Grand Prix on Oct. 12.
But Sergei Kolesnikov, a Russian biophysicist who campaigns to expose what he says is major corruption in the country, said during a visit to Washington this week that Sochi may not end up as the triumph Putin hopes it will be.
"I think underneath the Olympics drives many Russians crazy because the standard of life is decreasing," he said.
"Everyone is going to look back from this and remember only that $52 billion were thrown away for nothing ... Everybody knows how much money was stolen to make the Olympics happen, so what should we be proud of?" (Additional reporting by the Reuters Winter Olympics team in Sochi and Rosa Khutor and John Shiffman in Washington; Editing by Peter Rutherford)