Original "American Idol" champ Kelly Clarkson is the clear favorite to win "World Idol," the contest pitching 11 winners of the reality TV show from around the globe, PEOPLE reports from London, where the show is being taped this week.

But her performance also set off a rivalry between the U.S. and Canada, as American-based judge Simon Cowell slammed his Canadian counterpart Zack Werner, who declared that Clarkson had "shouted" rather than had sung parts of her rendition of her song, "Natural Woman."

During the program, which airs on FOX Dec. 25 (after which viewers will cast their vote for the winner, to be announced on a Jan. 1 show that will also feature a performance by Elton John), Cowell comes to blows with Werner, telling him, "You are not fit to judge her. There is a huge gulf (between Clarkson and the rest)."

British TV judge Pete Waterman (the man who launched Aussie sensation Kylie Minogue's career) applauded Clarkson, but added, "The thing that drives me nuts about you is how you go all over the place with all those trills and frills."

Clarkson took in his judgment and replied, "My Mom hates it when I trill." She also said she gets carried away with the emotion of it all and sings where the tunes take her.

After her performance and assessment at the hands of 10 judges (Cowell, as the U.S. representative, does not judge her), Clarkson told British presenters, Ant and Dec (real names: Anthony McPartlin and Declan Donnelly), that returning to the "Idol" stage was spine-tingling -- and that once again hearing the title music was "nightmarish."

Clarkson, 21, is pitted against another established star, 24-year-old Will Young from the U.K., and such lesser-known Idols as Norway's Kurt Nilsen, a former plumber.

The show also includes Diana Karzon, 19, who is representing the Pan Arabic region of 11 countries. She sang "Ensani Ma Binsak" in Arabic, which was praised by the judges for the fact that it brought her language to the contest.

Belgian Peter Evrard, 28, bravely tackled a hard rock anthem, Nirvana's "Lithium."

The newest Idol -- charismatic Guy Sebastian, 22, from Australia -- only won his country's contest five weeks ago but is considered a favorite. He sang a jaunty version of "What a Wonderful World."

Cowell, referring to the Australian's defeat by the English in the recent rugby world cup, told Sebastian: "After the fiasco of your rugby attempt, you made up for it."