By Mitch Phillips

RIO DE JANEIRO (Reuters) - Many sportsmen say they 'can't believe it' in the moment of achieving their lifetime goal but in the case of Adam Peaty, who posted another world record and won Britain's Rio first gold on Sunday, it seemed like he really meant it.

"I touched the wall and looked around and thought 'where is everybody?'" Peaty told reporters.

It was hardly surprising as he had just won the Olympic 100 meters breaststroke final with a world record and a remarkable 1.56 seconds ahead of second-placed South African defending champion Cameron van der Burgh.

"It's surreal to win it, to go 57.13 and to win GB's first medal. Honestly, I think you'll have to ask me about it in two days," he added.

Still only 21, Peaty came into the Games as a world, European and Commonwealth champion and the world record holder.

His stunning performance on Sunday has lifted him to a whole new level in the British sporting consciousness - or will do when most of the country wakes up.

Peaty is the country's first male Olympic swimming gold medalist for 28 years and only the fourth in last 100 years, following on from David Wilkie (1976) Duncan Goodhew (1980) and Adrian Moorhouse (1998) - all four of them breaststrokers.

However, none of that illustrious trio demolished the opposition the way Peaty has over two days in Rio.

His own 2015 world record of 57.92 seconds was brushed aside with a 57.55 in Saturday's heats and he was over a second faster in qualifying than anyone else in the final.

He knew he just had to keep his head and the result should look after itself but he is not the sort of competitor to sit back, and duly reacted fastest to the gun and smashed out another world best of 57.13.

"I can't really describe what it was like but coming home with that crowd roaring is what I've always dreamed of," he said.

"I was a bit anxious after the worlds last year but I put so much effort in to fixing my dive and it paid off. My stroke felt absolutely amazing tonight and I just kept pumping it through. That's probably the best-executed race of my life.

"I thought the best possible time I could achieve here might be a 57.3 but 57.1 - I have to slap myself. It's absolutely incredible."

Peaty, famously, was scared of water as a child, fighting his mother when she tried to get him near a bath and refusing to countenance a shower.

"Yep," he said, when questioned on it for about the 14th time this week. "I think you can say I've overcome that fear."

(Editing by Greg Stutchbury)