The flight will count as one sector only of the 16 allowed in the rules.
The rules also state that this would count as including Asia as a continent though. That is why it is impossible to buy a 3 continent xONEx ticket from Australia.
Originally Posted by OneWorld Explorer rules - section 4 (j)
Travel between Australia and Europe on a single flight number is considered travelling SW Pacific-Asia-Europe through three continents.
The complete rules can be found in the rule sheet link in the fare estimate section of
this page on the one world website.