LONDON – Anthony Joshua retained his world heavyweight titles with a ninth-round knockout of Kubrat Pulev on Saturday, potentially setting up an all-British fight against Tyson Fury to be undisputed champion of boxing's marquee division.Joshua had already knocked down Pulev three times when he unleashed a right hook that sent the 39-year-old Bulgarian to the canvas once again.This time, Pulev couldn't get up.After months of boxing fights in empty British venues, up to 1,000 spectators — a limited number that included boxing royalty in Floyd Mayweather — were inside Wembley Arena to see Joshua make his first defense of the WBA, IBF, WBO titles since regaining them in a rematch against Andy Ruiz Jr.Now he has done away with the durable but.