INDIANAPOLIS — Michael Phelps called it quits because of a sore neck at the U.S. nationals, leaving the spotlight to rival Ryan Lochte, who qualified today for the world championships later this month.

Phelps withdrew from the 100-meter freestyle heats in the morning on the advice of a doctor after waking up a day earlier with a kink on the left side of his neck. He swam through the pain to set a world record in the 100 butterfly on Thursday, but said he felt worse Friday despite receiving numerous treatments.

"It wasn't fun swimming the 100 fly with that," he said. "I could barely move my neck to breathe. I definitely didn't feel 100 percent."

The 100 free, in which Phelps owns the American record, was going to be his final event at nationals. He said he was willing to try, but his coach Bob Bowman vetoed the idea.

"We're going to err on the safe side," Bowman said.

Phelps qualified for the world championships in Rome, where he'll swim the 100 and 200 flys and the 200 free. He will likely swim on three relays, too.

Even if he had qualified, Phelps said he wouldn't have swum the 100 free at worlds because it conflicts with the 200 fly. The swimming events begin July 26, giving him two weeks to train.

Lochte qualified second-quickest in the 100 free heats, but he also withdrew to focus on the 200 individual medley.

Good idea.

Lochte won in 1 minute, 54.56 seconds — the second-fastest time ever in the event, trailing only Phelps' world record of 1:54.23 set at the Beijing Olympics. Lochte, who won silver in Beijing, was on a world-record pace through 150 meters before tailing off.

"I was pretty surprised," he said. "I looked at the video and I know there's a lot of improvement I can make, so hopefully worlds will be a lot faster. I feel like I can go at least a second faster."

Eric Shanteau, the third-fastest American ever, finished second in 1:56.00.

Lochte already qualified in the 400 IM and 800 free relay.

The absences of Phelps and Lochte from the 100 free opened things up for lesser-known Olympians Nathan Adrian and David Walters.

Adrian won in 48 seconds and Walters touched second in 48.17. Olympians Garrett Weber-Gale and Matt Grevers were third and fourth, ensuring themselves trips to Rome.

Two other Olympians, Cullen Jones and Ricky Berens, finished fifth and sixth, making it likely they'll be on the U.S. team, which is limited to 26 men and 26 women.

Weber-Gale and Jones tied for second in the 50 free and will duel one-on-one for the final spot in that event Saturday.

Adrian had already won the 50 free at the meet where he's broken out individually. Previously, the 20-year-old NCAA sprint champion was primarily a relay swimmer.

"It's very exciting," he said. "This is the year after the Olympics, this is when a lot of people start to step up and establish themselves as international swimmers."

Adrian's time didn't come close to Phelps' American record of 47.51.

"He's going to be there on the relay," he said of the 14-time Olympic gold medalist.

A couple of teenagers dominated the 200 backstroke. Elizabeth Beisel, a 16-year-old Olympian, won in 2:08.80 and Elizabeth Pelton, a 15-year-old from the same North Baltimore club as Phelps, was second.

Beisel had already qualified in the 400 individual medley.

"My strategy has been to bring it home the last 50," she said. "Knowing I had that extra gear in me helped a lot."

With Pelton likely securing a spot on the team, Beisel won't be the kid this time.

"They can't make fun of me," she said of her teammates.

Margaret Hoelzer, the Olympic silver medalist and former world record-holder, was third and failed to earn a trip to worlds.

Olympian Kathleen Hersey won the 200 fly in 2:06.44. Mary DeScenza, who didn't make the last two Olympics, finished second. Olympian Elaine Breeden was third, keeping her off the U.S. team for Rome.