BARCELONA, Spain — Matt Grevers scratched his head, wondering what went wrong.

Nathan Adrian and Ryan Lochte stared at the scoreboard, their jaws open in disbelief. Kevin Cordes stood on the deck with his hands on his head.

“That’s like a punch in the gut right there,” U.S. men’s head coach Bob Bowman said.

Moments earlier, all four swimmers were embracing each other, again celebrating that surest of gold medals in the pool — the men’s 400-meter medley relay.

It’s a race the U.S. has never lost, except for disqualification.

It happened again Sunday, as the American foursome had the gold ripped from their hands on the final day of the FINA World Swimming Championships.

Since the race’s inception at the 1976 Montreal Games, the Americans’ only defeat at a worlds or Olympics came at the 2007 worlds in Melbourne, Australia, when Ian Crocker dove too soon for the butterfly leg in morning heats.

This time, the disqualification came during the final session before a crowd of 10,000 screaming fans inside the sweaty Palau Sant Jordi. And after Adrian, the defending Olympic champion in the 100, touched the wall first in the anchor leg by nearly 1.5 seconds — an eternity in swimming — his last chance for gold slipped through his fingers.

“A relay disqualification is not a particular individual’s fault,” Adrian said. “It’s Team USA’s fault and it falls on all of our shoulders.”

Adrian went from celebration to disbelief in a matter of seconds after he touched the wall.

“It’s a bummer, man, a huge bummer,” Adrian said. “What are you supposed to do? I heard the French guys screaming and I was, ‘Wait a minute, what happened?’

“I think it’s a progress of emotions. Briefly, was it me? And now it’s about looking forward to next year.”

Cordes, a 19-year-old competing at his first worlds, dove for his breaststroke leg 0.04 seconds before Grevers touched the wall to complete his backstroke leg.

The rules allow a leeway of 0.03, so it was 0.01 over the limit — the smallest margin possible.

“It’s as much my fault or more than Kevin’s,” Grevers said. “The guy coming in is usually the one responsible. I kind of slipped off my start and got a little more tired than I wanted to at the end.

“I probably had a slower rate than I was anticipating — obviously than he was anticipating,” Grevers added. “I got to learn to finish better, and he’s probably got to learn to time a little better. I have a feeling Kevin’s going to be a little safe for the next couple years.”

When "DQ" was placed next to United States on the scoreboard, France moved up to take the gold, while the silver went to Australia and Japan snatched the bronze. The U.S.'s time was 3:30.06, but it mattered little.

"If us four ever step up again we're never going to have a disqualification, that's for sure," Adrian added. "It will really motivate him. I don't doubt if in the next couple years we're going to have the fastest breaststroker in the world swimming for Team USA. This could be a catalyst for that."

Adrian didn't live up to personal expectations this week in the Catalonia city along the coast of Spain. The Bremerton native finished with a bronze in the 100 free, getting nipped at the wall by teammate Jimmy Feigen and winner James Magnussen of Australia. Adrian finished fourth in the ultra-competitive 50 freestyle as well and the Americans settled for a silver in the 400 freestyle relay that kickstarted the meet.

Adrian came down with a stomach illness early in the meet and it was a battle to regain his strength and the momentum he had built earlier this year.

His relay split on the anchor was 46.69, a season's best. The time was also the fastest in a textile suit in history in a relay split.

"It was pretty good, it felt pretty good as well," Adrian said of his swim. "I didn't get caught up in the wash in a pool of big guys swimming. Swimming in the middle of the pool is always tough, but thank God I went in a little bit ahead thanks to Ryan. It was a good relay."

Just like Adrian, much of the meet had been difficult for Cordes.

After winning the 100 and 200 breast at the U.S. trials, his best result here was seventh in the 100. He failed to advance from morning heats in the 50 and just missed qualifying for the final in the 200, finishing ninth and missing the cut by 0.02.

“It’s a big step up to come here,” Bowman said. “This is a great learning experience, because DQ-ing a relay in the first world championships of the quad is one thing, doing it in an Olympic prep competition would be 10 times worse, right? So it’s a good learning experience and they have to go back and rethink how they’re going to react to things in this environment and do better.”

America’s golden girl Missy Franklin climbed to the top of the podium one more time and claimed her record sixth gold medal, swimming the leadoff leg for the Americans in the 400 medley relay. Franklin gave the U.S. a slight lead in the backstroke, and her teammates — Jessica Hardy, Dana Vollmer and Megan Romano — made it look easy from there in a time of 3:53.23. Australia took the silver and Russia the bronze.

Franklin became the winningest female swimmer ever at a world meet, eclipsing the record that was shared by Tracy Caulkins, who won five times in 1978, and Libby Trickett, who did it in 2007.

Franklin was not even chosen as the top female swimmer of the meet. That award went to fellow American Katie Ledecky, who won four golds and set two world records.

China’s Yang Sun was honored as the top male swimmer after sweeping the freestyle distance events. He closed with a victory in the 1,500, adding to his titles in the 400 and 800. After dueling with Canada’s Ryan Cochrane most of the way, the Chinese star turned it on the last two laps and won going away in 14:41.15.

Cochrane took silver and Italy’s Gregorio Paltrinieri bronze. Americans Connor Jaeger and Michael McBroom finished off the podium in fourth and fifth.

In other events on the final night, Japan’s Daiya Seto held off American Chase Kalisz to end U.S. domination of the men’s 400 individual medley, Hungary’s Katinka Hosszu won the women’s 400 I.M., and Ranomi Kromowidjojo of the Netherlands took the women’s 50 freestyle.