Michael Phelps celebrated his 27th birthday by beating his great rival Ryan Lochte in their penultimate showdown before London 2012.

This was the third meeting between the pair this week and they battled stroke for stroke at the US Olympic trials in America's Midwest in the 200 metres individual medley.

Lochte beat Phelps in the 400m individual medley on Monday but Phelps avenged that loss winning in 54.84 seconds.

"It feels good to be back on that [winning] side," Phelps told reporters. "But I'm sure that's not going to be the end of us going back and forth."

Lochte had won the 200m backstroke final just 30 minutes before taking on Phelps and was just 0.11 seconds behind, setting the stage for another epic duel in London when both men will be at their peak.

"It doesn't really matter what happens here, the bigger races are a couple of weeks down the road," Phelps added.

"The next race is the one that counts, I know that, and that"s one thing that I"m looking forward to."

Phelps has already qualified for four events in London and looks certain to add a fifth after setting the fastest time in the semi-finals of the 100m butterfly.

With the addition of the three relays, he will swim the same eight events he contested at Athens and Beijing.