Backstroke specialist Matt Welsh spread his wings to embrace the world 50m butterfly record on a night of world records for Australia in the Barcelona pool.

Welsh, the defending world 100m backstroke champion, shocked even his coach Ian Pope as he registered 23.43s to take the gold.

Two races later, Leisel Jones set a new world time of 1m06.37s in her 100m breaststroke semi-final.

Welsh's shock performance in the one-lap butterfly event was 0.01s faster than defending champion Geoff Huegill's old world standard of 23.44s set in a semi-final at the last world titles in Fukuoka, Japan, two years ago.

"The first thing that went through my mind was: 'Oh my God, I've won. Oh my God, it's a world record," said Welsh, who only did the race as a novelty event.

Pope, who coaches Welsh in Melbourne, admitted he never thought the backstroke specialist would win.

"I felt he was a chance for a medal. I really didn't think he'd win it but when he puts his mind to things, he just lifts to another stage. It was fantastic," Pope said.

"After the race I just said: 'Fantastic. Where did that come from?' He said: 'I don't know'.

"He's just on cloud nine. He's feeling great."

Welsh came into the Barcelona meet pledging to attack American Lenny Krayzelburg's 100m backstroke record and will swim the final of that early Wednesday morning Australian time.

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