Sainz was deemed 'wholly to blame' for the first corner collision with Aston Martin's Fernando Alonso, who ended up third, at the final re-start of the triple red-flagged race.
Red Bull have now claimed all three Grand Prix wins in the new season, a record for the team, resuming their dominance after their runaway success in 2022.
Leclerc's car was dominant on the upgraded Albert Park circuit as the Monagesque sealed his fourth career win more than 20 seconds ahead of Red Bull's runner-up Sergio Perez.
Vettel is something of an Australian Grand Prix specialist, having won the race three times.
The season will now start in Bahrain on March 28.
The Chinese Grand Prix was supposed to take place at the Shanghai International circuit on April 19 but was postponed until later in the year because of the coronavirus outbreak.
Austria's races start the season on July 5 and 12 and will be called the Austrian Grand Prix and the Grand Prix of Steiermark (Styria), the region in which the circuit at Spielberg is located.
Formula One needs a minimum of eight races for the season to be a proper championship.
Formula One and the governing FIA said they expected to begin the championship in Europe at the end of May, subject to regular review.
The season-opener was scrapped hours before the first practice session was due to get under way after a McLaren team member tested positive to the virus.