The Real Madrid striker emphatically answered media speculation that he might be putting on weight as the world champions overtook their bitter rivals to go top of the South American group with one third of the competition completed.
"The goals were all normal, they were all penalties, and Ronaldo is still the player who makes the difference," Brazil coach Carlos Alberto Parreira told reporters in Belo Horizonte.
Colombia remained bottom after they were sunk by Franklin Salas's second-half winner in Quito, their fourth defeat in six outings.
Although Brazil and Argentina look firm favourites to take two spots, this week's results have left the other places wide open with only four points separating Argentina, second with 11 points from six games, and eighth-placed Uruguay.
Chile (10 points), Paraguay (10), Venezuela (9), Peru (8) and Ecuador (7) are sandwiched inbetween. Bolivia (6) are ninth with Colombia (4) bottom.
The top four teams qualify directly and the fifth plays off against the Oceania region winners for another place at the finals in Germany in 2006.
Brazil (12 points) are the only unbeaten team after yet another extraordinary Ronaldo performance, a happy return to form after Real Madrid's dismal season.
The striker had barely touched the ball when he burst into the penalty area in the 17th minute and was upended by Gabriel Heinze's late, sliding tackle.
Ronaldo took the penalty himself and sent his kick low to Pablo Cavallero's left only for it to be disallowed because his team mates were inside the area. For the retake, he converted an almost identical effort.
ARGENTINE PROTESTS
He stroked home his second in the 68th minute after being tripped by Javier Mascherano and completed his treble deep into injury time after falling over Cavallero's clumsy dive for the ball.
Juan Pablo Sorin pulled a goal back in the 80th minute and Argentina threatened to snatch a late point before Ronaldo had the last laugh.
"Ronaldo was the determining player in the game, I have nothing to object to in the refereeing," said Argentina coach Marcelo Bielsa, whose players surrounded Colombian referee Oscar Ruiz to protest at the end.
Former Southampton striker Agustin Delgado scored his first international goal since the 2002 World Cup to give Ecuador a third-minute lead against Colombia in Quito.
Frankie Oviedo equalised 10 minutes into the second half with an almost identical goal, a header from a corner, but Salas settled the match with a well-taken effort in the 66th minute.
Reinaldo Rueda, Colombia's second coach of the campaign, refused to be downhearted. "There's still a long way to go," he said. "We mustn't drop our heads."
