Parker has scored a majority points decision over Briton Hughie Fury in their 12 round title fight in Manchester.
Two judges had Parker winning 118-110, while the third had it 114-all.
All of the rounds were even with Parker unable to land the knockout blow while Fury spent the fight on the back foot to keep out of trouble.
He did however stay in contention with his job.
The judges would have favoured Parker's aggression, while Fury spent most of his time in defence.
25-year-old Parker takes his unbeaten record to 24 wins, while it is a first loss for 23-year-old Fury in 21 bouts.
Photo: Supplied / Photosport Hughie Fury and Joseph Parker