required just four rounds to knock out Billy Dib to claim the WBC international welterweight title in Saudi Arabia
The British fighter outgunned an inferior opponent in every department at the King Abdullah Sports City in Jeddah, and in doing so keeps alive hopes of facing Manny Pacquiao in the ring.
Dib's corner threw in the towel after Khan showed his hand speed to floor the Australian for the second time with a flurry of body shots.
Former world champion Khan had earlier signalled his intent by putting Dib on the canvas with a superb left hook in the second round.
The 32-year-old from Bolton was back in the ring for the first time since his controversial WBO welterweight title defeat to Terence Crawford in April.
He was originally scheduled to meet Neeraj Goyat.
But Indian Goyat was forced to pull out after suffering serious injuries in a car accident in June, leaving Dib, a former IBO super-featherweight and IBF featherweight champion, to move up the weights and step in.
The 33-year-old Dib had announced his retirement after a points defeat to Tevin Farmer in an IBF super-featherweight bout in Sydney last August.
He struggled to make an impact on his return in a bout which was one-sided from the opening bell, and was comfortably beaten after failing to cope with the superior skills of Khan.