Gomez's left hook had rattled Khan in the second round
Amir Khan survived an early knockdown as he successfully defended his Commonwealth lightweight title against Michael Gomez in Birmingham.
The 21-year-old was floored by a powerful left hook from Gomez in the opening exchanges of the second round.
But Khan, who had his opponent on the canvas in the opening round, countered with a series of powerful punches.
Gomez was floored once more in the fifth and referee John Keane stopped the fight after a big Khan right hand.
The brutal encounter was by far the toughest of Khan's 18-fight professional career.
The Bolton-born fighter had begun in confident style, breaking Gomez's guard with a flurry of combinations, culminating in a huge right hand to send his opponent to the canvas.
But Gomez - celebrating his 31st birthday - refused to surrender and began the second round began in complete contrast to the first.
He sent Khan tumbling with a blistering left hook which stunned Khan - and the packed crowd - at the National Indoor Arena.
"I got caught with a left hook and I dropped my hands but I didn't make that same mistake again," Khan admitted.
"It was one of those flash knockdowns but I got straight back up."
Khan immediately counter-attacked and cut the former British super-featherweight champion above the left eye.
The ferocity continued in the third round and the fourth saw Gomez plant a vicious left hook to the body, which hurt Khan badly.
Sensing his vulnerability, Gomez targeted Khan's midriff for special attention, but Khan once again used his speed to hit back with yet another series of bruising combinations.
But despite the assault, Manchester fighter Gomez was still sitting in his corner at the end of round four.
However, a left to the body in the fifth saw Gomez drop to the floor for the second time before a succession of left and right hands saw referee Keane intervene, much to the dismay of Gomez.
"He is a world class fighter with world class vulnerabilities but his hand speed beat me," said Gomez, known as "The Predator".
"I don't think I performed too well in the biggest chance of my life."
Khan, meanwhile, believes he will benefit from a tough examination of his credentials.
"This was one of my toughest fights but I learned from my mistakes,' he added. "I will watch the video and work on them and continue my journey to the world title."