Amir Khan was made to work hard before beating Scotland's Willie Limond to win the Commonwealth lightweight title.
Khan survived a scare before maintaining his unbeaten record
Khan had looked in control early on in their fight at London's O2 Arena but Limond rocked the 20-year-old in the sixth round, knocking him to the floor.
The Bolton fighter recovered and dug deep to force his opponent to take a count in the next round.
Khan dominated after that and Limond was forced to retire after the eighth round with nose and jaw injuries.
The Athens silver medallist came into the fight with nine knockouts from his 12 pro fights but this was by far his toughest test.
He played a patient game early on and seemed to have a narrow advantage over his more experienced opponent.
Although he picked off Limond with a series of jabs in the second round, the 28-year-old Scot kept Khan on his toes, especially in round five when a right hand connected cleanly.
But the fight sparked into life in the sixth round when Limond seized the upper hand and landed with a volley of punches which sent him sprawling.
Somehow Khan struggled through the remainder of the round and the knockdown seemed to spark him into action.
The seventh round was far more one-sided as Khan backed Limond against the ropes with more hurtful combinations and the champion went down himself.
By the eighth, Limond was in trouble, but the Scot refused to give in and had to be withdrawn by his corner, handing Khan the toughest victory of his career.
"The timing just wasn't there," Khan admitted afterwards. "I was over-anxious and wanted to commit myself too much. I was running inside, made a mistake and got caught with the right hand.
"It could have changed the fight but it didn't - it shows I've got a good chin. I just had to compose myself.
"Good fighters go down, come back up and knock the other person down and I did that. I wanted that title more than Willie did."