Alonso was linked to five teams for a race seat in 2003 and was strongly favoured to replace Button at Renault.
Briatore promoted him to its race team for 2003.
Alonso trained in Kenya with the team on a fitness programme in late 2002 to prepare for the season.
He said his stint as a test driver had prepared him and felt pre-race testing would better acquaint him with the tracks.
Alonso felt confident driving the R23 which responded adequately to setup changes and its Michelin tyres allowed him to use extra aggressive race strategies.

At the season's second round, the Malaysian Grand Prix, Alonso took his first career pole position, becoming Formula One's youngest pole sitter at 21 years and 236 days.
He took consecutive third-place finishes in Malaysia and Brazil; Alonso had a 270 km/h (170 mph) accident in Brazil, sustaining a bruised left elbow, knee and thigh.
He then finished second at the Spanish Grand Prix and eclipsed Bruce McLaren's record as Formula One's youngest driver to claim a race victory when he won the Hungarian Grand Prix from pole position aged 22 years and 26 days.
Alonso finished the year sixth overall with 55 points scored and four podium finishes.

He remained with Renault for 2004.
Alonso regularly travelled to Renault's factory in Enstone, England during the R24's construction and discussed a large amount of information with his engineers during the off-season.
He felt confident with the car the first time he drove it: Alonso described the R24 as quicker than the R23, having a similar steering style and found it not too difficult to become acquainted with.
Alonso said his objective for 2004 was to improve from the 2003 season but recognised the difficulty of the task.
Alonso had a consistent year with four podium finishes, a pole position at the French Grand Prix and no race victories.
He finished in fourth place in the drivers' championship with 59 points.
Alonso was linked to five teams for a race seat in 2003 and was strongly favoured to replace Button at Renault. Briatore promoted him to its race team for 2003. Alonso trained in Kenya with the team on a fitness programme in late 2002 to prepare for the season. He said his stint as a test driver had prepared him and felt pre-race testing would better acquaint him with the tracks. Alonso felt confident driving the R23 which responded adequately to setup changes and its Michelin tyres allowed him to use extra aggressive race strategies.
At the season's second round, the Malaysian Grand Prix, Alonso took his first career pole position, becoming Formula One's youngest pole sitter at 21 years and 236 days. He took consecutive third-place finishes in Malaysia and Brazil; Alonso had a 270 km/h (170 mph) accident in Brazil, sustaining a bruised left elbow, knee and thigh. He then finished second at the Spanish Grand Prix and eclipsed Bruce McLaren's record as Formula One's youngest driver to claim a race victory when he won the Hungarian Grand Prix from pole position aged 22 years and 26 days. Alonso finished the year sixth overall with 55 points scored and four podium finishes.
He remained with Renault for 2004. Alonso regularly travelled to Renault's factory in Enstone, England during the R24's construction and discussed a large amount of information with his engineers during the off-season. He felt confident with the car the first time he drove it: Alonso described the R24 as quicker than the R23, having a similar steering style and found it not too difficult to become acquainted with. Alonso said his objective for 2004 was to improve from the 2003 season but recognised the difficulty of the task. Alonso had a consistent year with four podium finishes, a pole position at the French Grand Prix and no race victories. He finished in fourth place in the drivers' championship with 59 points.
Motor racing career of Fernando Alonso