WATCH: Deontay Wilder's BRUTAL first round KO as he challenges Anthony Joshua to fight

The gobsmacking clip shows Wilder, 32, batter 39-year-old Stiverne repeatedly – leaving him flailing on the floor. And the boxing star has challenged Anthony Joshua to what would be a huge match-up. After knocking his opponent out in a brutal first round at the Barclays Center in New York, the US boxer called out to his Brit rival. He said: "I declare war on you. Do you accept my challenge?" There appeared to be no contest between Wilder, who is unbeaten in his professional career, and Stiverne, who was sent crashing to the canvas three times before the referee called time on last night’s fight in the first round. After his sixth title defence, Wilder now has 39 undefeated fights and 38 KOs to his name and wants to unite the heavyweight titles. Asked by Showtime Sports about fighting IBF and WBA champion Joshua, 28, he said: "I've been waiting on that fight for a long time now. "I declare war upon you. Do you accept my challenge? I've been waiting for a long time. I know I'm the champion. I know I'm the best. Are you up for the test? "A king doesn't chase the peasants. A king takes kings. I want Joshua. If he doesn't give me the fight we have other plans. "The world wants Joshua, the world wants Wilder, I want Joshua. Joshua come and see me baby. No more dodging, no more excuses. Make the date, don't wait."