Cook suffered the second loss of his career

Maesteg's Cook opened confidently, looking to off-load powerful left hooks, but Rios looked classier and landed with some sharp counter-shots.

The challenger began to off-load in the second, shaking Cook with a right.

A straight right dropped Cook in the third, the Welshman climbing to his feet but proving defenceless from the next attack as the referee stopped it.

The loss was just the second of Cook's career, taking the 29-year-old's record to 23-2-0 (10 KOs).

I had a setback earlier in my career and came back with 18 good wins, so I'll be back this time Jason Cook

Thirty-year-old Rios' record moves to 39-3-0 (8 KOs), this proving his first win outside Argentina, although each defeat was against world-class opposition.

Cook vowed to come back from the defeat, saying: "I took things a bit easy and got caught cold more than anything.

"This may have been a step too far, but I'll be back.

"I made the weight all right, but maybe it's time to step up, I'm strong enough to carry my weight.

"I had a setback earlier in my career and came back with 18 good wins, so I'll be back this time."

On the undercard, Hereford's Dazzo Williams retained his British featherweight title - and claimed a Lonsdale Belt - with a highly controversial points win over John Simpson.

Williams won the first two rounds before the Scot found his feet and appeared to dominate the rest of the fight, but referee Phil Edwards - in charge of his first title fight - awarded the home fighter a 115-114 verdict.

Pembroke Dock heavyweight prospect Scott Gammer scored the best win of his career with a second-round stoppage of experienced Pole Roman Bugaj.