Ryan Lochte tonight deposed Michael Phelps as the Olympic 400 metres individual medley champion as he secured a dominant victory in London.

The Aquatics Centre also bore witness to the first women's long-course world record since the ban on performance-enhancing suits, with Ye Shiwen lowering the 400m individual medley mark with an astonishing last two lengths.

Ye's fellow Chinese athlete, Sun Yang, was just seven hundredths of a second outside the 400m freestyle world record, his apparently languid stroke helping propel him to the Olympic title while Australia set a new Olympic mark to win the women's 4x100m freestyle relay.

The men's 400m medley was meant to be the first instalment of a showdown between Lochte and Phelps but ultimately the former was never threatened and touched in four minutes 05.18 seconds.

Brazil's Thiago Pereira was second with Japanese 17-year-old Kosuke Hagino third, just a year after taking bronze at the World Junior Championships.

Phelps was third at the halfway stage before dropping out of the medals on the breaststroke leg, the Baltimore swimmer unable to claw back the deficit to finish fourth.

Phelps pulled no punches about his performance, saying: "Just a crappy race.

"I felt fine for the first 200. I couldn't really go in the last 100.

"Frustrating. That's all I can say. It's pretty upsetting. But I think the biggest thing now is just to try to get past this and move forward.

"I have a bunch of other races and hopefully we can finish a lot better than we started. That's what I'm going to try to do."

For Lochte, his emotions were in complete contrast.

"Going into the race, I was so excited to get a final, so I went a little too hard in the first 50 of the fly.

"I kept looking at the scoreboard, I knew it wasn't going to be just me and Michael - there were other great swimmers in the race.

"When I hit the wall I was in shock, I think I still am, to have won."

Of Phelps, he added: "It's weird not having Michael with me on the podium, I don't know if this puts me as one of the world's greatest, that is not my decision.

"But to me he is one of the greatest, whatever happens he will be remembered as one of the greats."

Barry Murphy was the first Irish swimmer in the London pool when he contested this morning's heats of the 100m breaststroke, but there was disappointment for the Dubliner as he exited the competition after finishing eighth.

The 26-year-old's time of 1:01.57 was his second-fastest ever in the event but it was not enough to earn him a qualifying spot.

However, Murphy will get another opportunity at the Aquatics Centre when he returns for the heats of the 50m freestyle on Thursday. 

In the 400m freestyle, Sun finished in 3:40.14, an Olympic record and just outside Paul Biedermann's 2009 mark which is a great illustration of the benefit turbo suits offered at the end of races.

Ye produced an astonishing final 100m of 58.68 to lower Stephanie Rice's 2008 world record in the women's 400m IM.

Second at the final turn behind world champion Elizabeth Biesel, the 16-year-old powered away to take 1.02secs off Rice's mark.

Biesel was second, with Ye's compatriot Li Xuanxu third.

Australia set a new Olympic record of 3:33.15 to win the women's 4x100m freestyle relay.

Cameron van der Burgh set a new Olympic record of 58.83 to qualify fastest into the 100m breaststroke final while Dana Vollmer looked fearsome going into the 100m butterfly final in 56.36.