Warrington, who is also Commonwealth and European champion, continued his progress to make it 23 wins out of 23 and to set up the prospect of a world title fight with Wales’ current IBF champion Lee Selby.
Warrington made a very bright start in the opening round by landing several decent shots on Amagasa who himself threw a few decent punches but was outboxed and out-speeded.
It was a similar story in round two with Amagasa twice on the ropes for many seconds in a round in which Warrington landed one really good right hander.
There was a slightly less ferocious start to round three but the round still ended with Warrington hammering Amagasa in the corner.
Round four was possibly Amagasa’s best yet but only because of damage limitation and Warrington was again less dominant in round five with Amagasa having seemingly weathered the early storm.
The Japanese fighter then landed a few shots in round six as his improvement continued, not that Warrington looked in any danger.
Round seven proved uneventful and rather even but Warrington was back on top in round eight in which he landed a few notable clear punches.
Warrington continued to probe away in round nine and while Amagasa rallied towards the end of the round, some of his punches were a tad wayward and wild.
And Warrington then turned up the heat towards the end of round ten in which he was especially dominant in the latter stages before round 11 then proved the most dramatic yet.
Amagasa caught Warrington with a flurry of punches at the start of the round but a clearly annoyed Warrington came storming back to dominate the round and open up a cut above his opponente’s eye.
Both fighters then went hell for leather for the glorious finish in the final round with a gutsy Amagasa refusing to throw in the towel but Warrington landed a couple more good shots and the damage was done.
It was quite clear that Warrington had done more than enough to secure a victory and he was duly awarded a unanimous victory 117-111, 118-111, 120-107.