The Real Madrid striker put the world champions ahead in the first half on Wednesday night with a twice-taken penalty after being upended by Gabriel Heinze.

Ronaldo 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 goalkeeper Pablo Cavallero's clumsy dive for the ball.

Juan Pablo Sorin pulled one back in the 80th minute as Brazil went top of the South American qualifying group and Argentina slipped to second after losing their unbeaten record.

Brazil have 12 points from six games and Argentina 11. The top four teams qualify for the 2006 finals in Germany and the fifth plays off against the winners of the Oceania group.

Argentina's players surrounded Colombian referee Oscar Ruiz to protest at the end but Brazil coach Carlos Alberto Parreira said there was nothing to argue about.

"The goals were all normal, they were all penalties, and Ronaldo is still the player who makes the difference," he told reporters.

Ronaldo, three times voted FIFA's World Player of the Year, had barely touched the ball when he burst into the penalty area in the 17th minute and was felled by Heinze's late, sliding tackle.

The striker took the penalty himself and sent his kick low to Cavallero's left only for it to be disallowed because his team mates were inside the area. For the retake, Ronaldo converted an almost identical effort.

Although Ronaldo and Kaka delighted the crowd with their trickery, Brazil went off the boil and Argentina created several chances by exploiting the home team's weakness in the air.

Hernan Crespo headed over from a corner and Sorin fired over from close range after Brazil again failed to clear a high ball.

At the other end, Luis Fabiano, standing in for the injured Ronaldinho, miscued after Kaka found him in the penalty area while Roberto Carlos threatened with a rasping 35-metre free kick measured at 123 kph.

Argentina were still threatening an equaliser when Ronaldo struck again in the 68th minute. He picked the ball up 35 metres from goal, ran past two defenders, was upended by a late tackle from Mascherano and this time sent Cavallero the other way.

The crowd were chanting "Ole" until Sorin headed home from a rebound after Pablo Aimar's header hit the post following another cross into the Brazil area.

Javier Saviola and Heinze went close to equalising but it was Ronaldo who had the last laugh, tripping over Cavallero's outstretched arms and slotting home his third penalty in the sixth minute of injury time.

"Actually, it was four penalties," he said.

"It was wonderful, marvellous."