Michael Phelps regained his golden touch on Wednesday with a record-setting triumph in the men's 200m butterfly at the swimming World Championships.

Phelps finally caught the wave of world records washing over these worlds with a time of 1min 51.51sec - and he didn't even need a polyurethane bodysuit to do it.

"I'm happy," Phelps said after bouncing back from his stunning defeat in the 200m free on Tuesday. "It was something that I really wanted to do last year, to break the 1min 52sec and coming into the night I just said I'm going to go for it and whatever happens, happens."

Phelps's world record was one of seven on the day, taking the tally at the halfway point of the eight-day competition to 22.

Zhang Lin became the first Chinese man to capture World Championship swimming gold, destroying Aussie distance great Grant Hackett's 800m freestyle world record.

Italy's Federica Pellegrini thrilled her legion of fans at Rome's Foro Italico with a victory in the 200m free, lowering the world record for the second time in two days with a swim of 1:52.93.

South Africa's Cameron Van Der Burgh also notched his second world record in as many days with his triumph in the 50m breaststroke in 26.67.

America's Mary Descenza threw in a world record in the heats of the women's 200m butterfly for good measure, and in the women's 50m backstroke semi-finals Daniela Samulski lowered her own world record with a time of 27.39 in the first semifinal only to be pipped by Anastasia Zueva's 27.38 in the second semi.

The record tally has already risen past the 15 set at the 2007 World Championships, and is closing in on the 25 posted at the Beijing Olympics.

But this time Phelps, still swimming in the Speedo LZR suit that has been overtaken by the polyurethane marvels unveiled this year, hadn't been at the forefront.

The 14-time Olympic gold medallist was upset in the 200m free on Tuesday, when Germany's Paul Biedermann took both his world title and world record.

The 24-year-old American had seemed non-plussed by his first defeat in world and Olympic competition since 2005, but he knew just what to do after the victory, raising both arms in celebration as he stood on the deck to acknowledge the cheers of the crowd.

"I do so many races that I can't get caught up in one event," Phelps said. "Last night, yeah, I was disappointed I didn't win. But I knew I had to put that behind me to get ready for tonight."

Phelps wasn't even wearing a bodysuit, going at the last minute with a waist-to-ankle version of the Speedo after his bodysuit felt too tight.

"This is what I've always worn in this race," Phelps said.

Suits or no, Phelps was never threatened as Poland's Pawel Korzeniowski and Japan's Takeshi Matsuda dueled for silver behind him.

"I tried to push on in the first 150 and get into as much open water as I could and then tried to just come up and last long," Phelps said.

Matsuda was lying second to Phelps until the final lap, when he was overtaken by Korzeniowski, who snatched the silver in 1:53.23 as Matsuda settled for bronze in 1:53.32.

Coach Bob Bowman said he knew Phelps was suffering at the finish.

"He swam a really fast first 150 and he paid for it a little on the last lap," the coach said. "I'm sure he'll be tired, but I knew nobody was getting by him. That's how he is."

Zhang turned in an astonishing swim, slicing 6.53sec off the previous world record of 7:38.65 set by Hackett at the 2005 World Championships in Montreal.

Despite the blazing pace of the race, Zhang had enough at the end to pull away from Tunisian Oussama Mellouli, the defending 800m world champion and reigning Olympic 1500m champ. Mellouli took silver ahead of Canadian Ryan Cochrane.

"I'm more than five seconds quicker than Hackett's record and I'm still surprised," Zhang said. "I can't believe it."