Deontay Wilder paved the way for a megafight with Anthony Joshua with a brutal stoppage of Luis Ortiz in New York.
But the Bronze Bomber did not have it all his own way in a rollercoaster clash against the previously undefeated Cuban.
Wilder, who had ended all but one of his previous 39 wins inside the distance, seemed to be sailing to another knockout win when he dropped Ortiz late in the fifth round.
But the challenger rallied during a huge seventh round and appeared to have his American opponent out on his feet when the bell went.
The tense clash then swung wildly once more in a mad 10th round which had Ortiz down and out with just 55 seconds left until the bell.
The final blow was a crippling uppercut which sent Ortiz down to his knees, giving referee David Fields no choice but to wave it off instantly.
Watch highlights of the bout below;