The 70-lap race was won from pole position by Fernando Alonso, driving a Renault, with Drivers' Championship rival Kimi Räikkönen finishing second in a McLaren-Mercedes and Michael Schumacher third in a Ferrari.
At the start of the weekend, McLaren and Renault appeared to be the fastest teams, topping the time sheets for both practice sessions on Friday.
However, Kimi Räikkönen suffered an engine failure, using a new-spec Mercedes V10, and was forced to drop ten grid positions as a result.
[3] Fernando Alonso scored his second consecutive pole position, with Toyota's Jarno Trulli alongside him on the front row.
The Saubers of Felipe Massa and Jacques Villeneuve were 10th and 11th respectively (subsequently promoted to 9th and 10th), while Williams, who had struggled all weekend despite several new aerodynamic updates to the car, were 13th and 14th.
[3] The start of the race saw Alonso speed away quickly, leaving Trulli to fend off Michael Schumacher through the first few corners, while Rubens Barrichello leap-frogged Takuma Sato into fourth place.
With all but the top four cars lapped, Sato ran wide briefly into the gravel at Estoril corner, which cost him 10th position to David Coulthard.
Button came in fourth to score BAR's first points of the year, with Trulli, Fisichella, Ralf Schumacher and Villeneuve completing the top eight.