JT fended off the fast-rising Bruno Mars - who was up five places to No 2 with When I Was Your Man.
Bastille fell one place to No 3 with Pompeii, with Pink and Just Give Me A Reason (ft. Nate Reuss) up six to No 4.
Thrift Shop by Macklemore (ft. Ryan Lewis & Wanz) was at No 5.
The Official UK Top 10 Singles...
1 (1) Justin Timberlake - Mirrors 2 (7) Bruno Mars - When I Was Your Man 3 (2) Bastille - Pompeii 4 (10) Pink - Just Give Me A Reason (ft. Nate Reuss) 5 (4) Macklemore - Thrift Shop (ft. Ryan Lewis & Wanz) 6 (3) One Direction - One Way Or Another (Teenage Kicks) 7 (-) Bridgit Mendler - Ready Or Not 8 (5) Aviici vs Nicky Romero - I Could Be The One (Nicktim) 9 (8) Baauer - Harlem Shake 10 (6) Taylor Swift - I Knew You Were Trouble