The X Factor judge teamed up with Lupe Fiasco for new cut 'Battle Scars', which went straight to the Aussie top spot in its first week on sale.
Justice Crew slip to two with 'Boom Boom', Maroon 5 are at three with 'One More Night', fun. are at four with 'Some Nights' and Owl City and Carly Rae Jepsen round off the Top 5 with 'Good Time'.
Taylor Swift lands at 13 with 'We Are Never Ever Getting Back Together', while Delta Goodrem enters at 15 with 'Dancing With A Broken Heart'.
Birdy climbs 15 places to 20 with 'People Help The People', Nicki Minaj slides to 32 with 'Pound The Alarm' and Mumford & Sons' 'I Will Wait' debuts at number 38.
The Top 10 singles in full (click where possible for our reviews):
1. (-) Guy Sebastian ft. Lupe Fiasco: 'Battle Scars'
2. (1) Justice Crew: 'Boom Boom'
3. (2) Maroon 5: 'One More Night'
4. (3) fun. 'Some Nights'
5. (5) Owl City ft. Carly Rae Jepsen: 'Good Time'
6. (4) Florence + the Machine: 'Spectrum (Say My Name)'
7. (6) Rudimental ft. John Newman: 'Feel The Love'
8. (9) Calvin Harris ft. Example: 'We'll Be Coming Back'
9. (11) Ed Sheeran: 'Drunk'
10. (7) Pink: 'Blow Me (One Last Kiss)'
Listen to Guy Sebastian's 'Battle Scars' below: