Ruas debuted in Ultimate Fighting Championship at the UFC 7 event. He firstly faced Larry Cureton, who outweighed him by 40 lbs, but Ruas submitted him with a heel hook after a methodical grapple. His next opponent was the judoka Remco Pardoel, who early tried a guillotine choke, but Ruas blocked it and grinded him with foot stomps. After a failed heel hook attempt, Ruas controlled Pardoel and attacked him with knees and punches on the ground, making him tap out. Ruas's final fight was against 6'8", 330 lb Paul Varelans, and he showed his muay thai skills by overwhelming Varelans with punch combos and repeated leg kicks. He also used again his characteristic foot stomps when Paul clinched him against the cage. At the end, Varelans could not take more kicks to his legs and fell to the ground, where Ruas pounded him until the referee stopped the fight, giving Ruas the victory of the tournament.