The track, which has now topped the charts in ten countries, pushes previous leader Guy Sebastian down to two with 'Battle Scars'.
Meanwhile, The Script leap nine to five with 'Hall Of Fame', Ne-Yo's 'Let Me Love You' rises 11 to six, and Rita Ora lifts 15 to ten with 'R.I.P'.
Further down the chart, Alicia Keys jumps 20 to 15 with 'Girl On Fire', Havana Brown's 'When The Lights Go Out' bounds 30 to 18, and Taylor Swift debuts at 20 with 'Begin Again'.
James Morrison rebounds 49 to 21 with 'I Won't Let You Go', Pink's 'Blow Me (One Last Kiss)' re-enters at 29, and Swedish House Mafia climb 40 to 30 with 'Don't You Worry Child'.
Elsewhere, Of Monsters And Men's 'Little Talks' jumps 41 to 32 and The Collective's 'Footloose' is new at 41.
The top ten singles appear below (click for our reviews where possible):
1. (2) Psy: 'Gangnam Style'
2. (1) Guy Sebastian ft. Lupe Fiasco: 'Battle Scars'
3. (3) Birdy: 'Skinny Love'
4. (4) Flo Rida: 'I Cry'
5. (9) The Script ft. will.i.am: 'Hall of Fame'
6. (5) Taylor Swift: 'We Are Never Ever Getting Back Together'
7. (6) Owl City ft. Carly Rae Jepsen: 'Good Time'
8. (11) Ne-Yo: 'Let Me Love You (Until You Learn To Love Yourself)'
9. (7) Justice Crew: 'Boom Boom'
10. (15) Rita Ora ft. Tinie Tempah: 'R.I.P'
Watch Psy's 'Gangnam Style' video below: