Alonso claimed his second victory in three races this season when he established an early lead then held off McLaren's Kimi Raikkonen on a dramatic afternoon at Melbourne's Albert Park.
Michael Schumacher was among a handful of drivers who were involved in high-speed crashes when he slammed his Ferrari into a wall about halfway through the race.
Officials introduced the safety car on four separate occassions to clear the track of debris as almost half the field failed to complete the race.
Ralf Schumacher successfully avoided the carnage to finish third in a Toyota ahead of fellow German Nick Heidfeld in a BMW Sauber.
Alonso's Italian team mate Giancarlo Fisichella, winner of last year's Australian GP and last month's Malaysian GP, finished fifth while Canada's Jacques Villeneuve was sixth for BMW Sauber.
Britain's Jenson Button, who started on pole position, would have finished fourth but his Honda engine blew up less than 100 metres from the finish line and he pulled over.
Alonso has 28 points to Raikkonen and Fisichella's 14.
Renault, winner of all three races so far this season, lead the constructors' standings with 42 points to McLaren's 23.
REUTERS PV RK1148