The 26 year-old, although dominant throughout, was made to work for the win and eventually sealed the triumph in the seventh round.
Breazeale was rocked a couple of times early on, but the Californian, 30, proved that he can take a dig as Joshua picked and probed with solid shots.
Joshua went to the halfway point in a fight for only the second time in his career, getting the job done with a flurry of punches the dropped Breazeale twice in quick succession.
Referee Howard Foster waved the contest off with Breazeale in no position to continue and handed Joshua a 17th straight knockout to extend his perfect record.
A fight with mandatory challenger Joseph Parker looms on the horizon for ‘AJ’ in the near future, although his deal with US network Showtime may see another challenger from across the Atlantic make the trip to Joshua’s backyard before a meeting with the powerful New Zealander.
Once again, Joshua looked an assured champion in front on his home crowd at the O2 Arena and it will take a lot for someone to dethrone the Londoner on current form.