It hasn't taken long for British triathlete Alistair Brownlee's halo to slip, although the evidence against him is hardly conclusive.

Brownlee, the Olympic gold medallist, won world acclaim after helping his brother Jonny cross the finish line in the final World Triathlon Series' race in Mexico.

But Spain's Mario Mola claimed that Alistair Brownlee used dirty tactics against him during the swimming leg, the Telegraph reported.

"I don't know who pulled off my cap and goggles during the swimming stage, but I am almost certain it was the older Brownlee," Mola told Spanish radio station Cadena Cope.

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"I would swear it was him because I looked to my left side from where the contact came and there was Alistair. I want to think it wasn't intentional but it wouldn't be the first time they [the Brownlees] tried to gain an unfair advantage."

Mola won the world title after finishing fifth in the Mexico heat and says Jonny Brownlee congratulated him, but Alistair did not.

"I have always had a good relationship with Jonny; he's a perfect sport," the 26-year-old from Mallorca said.

Spain's protest against Olympic silver medallist Jonny Brownlee, for using unfair assistance, was thrown out. Jonny was exhausted and staggering while leading with about 700m left when his brother stopped to assist him home. He thanked his brother for "incredible loyalty".