By Steve Keating

OMAHA, Nebraska (Reuters) - Michael Phelps had no appetite for a rematch with Ryan Lochte in the 400 meters medley so left it to the swimmer he calls his little brother to beat up on an old foe at the U.S. Olympic swim trials on Sunday.

Displaying the same ruthless competitive streak as his training partner Phelps, Chase Kalisz showed no mercy as he delivered an emphatic knockout punch to the wounded Lochte, pulling away from the 2012 London Summer Games gold medalist over the final two legs to become the first American swimmer to collect his ticket to Rio.

For more than a decade, Phelps and Lochte have engaged in some epic battles in the pool, the showdowns forging one of swimming's great rivalries.

Phelps won the 400 IM title at the 2004 Athens and 2008 Olympics while Lochte grabbed top spot on the podium in London.

But now aged 30 and bidding for a spot on his fifth Olympic team, Phelps wanted no part of the punishing 400 IM, instead passing the torch to Kalisz, who will carry it to Rio in August and an expected showdown with the Japanese double medal threat of Kosuke Hagino and Daiya Seto.

"I was so happy for Chase, I was crying when I was hugging him," said Phelps, who now trains in Arizona with Kalisz under coach Bob Bowman. "We kept the 400 IM in the MBAC (Maryland Baltimore Aquatic Club) family, it's in a safe place.

"He is like my brother and watching him to be able to do that is a very special moment.

"There was actually a time when he asked Bob if he could back off a little bit but I just see potential and I want him to be the best he can be."

Taking on the role of older brother, the 18-time Olympic champion, as demanding on Kalisz as he is on himself, has not been shy sharing his opinions when it comes to what he expects in and around the pool.

Even Bowman, a tough task master, felt sympathy for Kalisz, who has been routinely exposed to Phelps's other-worldly standards.

"When Michael gets on you, it's pretty severe," said Bowman. "It's kind of like nonstop for a while.

"When I do it it's like a nuclear bomb got dropped on your head for about two and a half minutes, but after that it's over.

"Michael kind of keeps it going. So I think it really pushed him (Kalisz) and really got him out of his comfort zone."

Like most competitive swimmers, Kalisz has lived in Phelps' long shadow but it is a place he has always felt comfortable.

"Michael told me how proud he was of me and that meant a lot," said Kalisz. "Michael is the greatest of all time, and I know no matter what I do I will never top his accomplishments.

"I'm looking forward to seeing him swim later in the week, I

know he's going to do awesome."

(Editing by Andrew Both)