Ryan Lochte's rivalry with Michael Phelps was billed as one of the big sporting attractions of London 2012.
The Americans - two of the strongest all-round male swimmers the sport has ever seen - were expected to fight out an epic Olympic duel at the Aquatic Centre.
In reality, the 400m individual medley turned into something of an anti-climax as Lochte eased his way to gold and Phelps, who won a record-breaking eight golds in Beijing, struggled home in fourth.
Here, BBC Sport examines the significance of Saturday's result.
Was Lochte's victory a surprise?
"I knew Lochte was at the top of his game, but Phelps looked like he had something in the bag from his trials. It's ended up being a damp squib," Steve Parry, a 2004 Athens bronze medallist for Britain, told BBC Sport.
Phelps had insisted he was finished with the 400m individual medley after his 2008 success in the event, regarded as the toughest in swimming as it involves backstroke, breaststroke, butterfly and freestyle.
True to those words, he focused on other races in the last two World Championships, but then sprang a surprise at the US Olympic trials in June.
Not only did he enter the event, he also qualified for London 2012, finishing second behind Lochte.
"Lochte is full of confidence at the moment and I thought Phelps looked very nervous before the race," said Parry. "I just question whether he [Phelps] ever thought that he could win it."
Lochte certainly had no such doubts.
"This is my year. I can feel it," he said. "I have trained my butt off for four years and there is no better way than to start with an Olympic gold."
What about the performance of Phelps?
The 14-time Olympic gold medallist was disappointed with fourth place, with coach Bob Bowman blaming poor preparations since Beijing.
"It was just a crappy race," said Phelps, who says this will be his last major championships. "I felt fine the first 200, then I don't know. They just swam a better race than me, a smarter race than me and were better prepared than me. That's why they're on the medal stand."
Bowman said: "His backstroke wasn't very good. I thought his breaststroke was credible, but his freestyle was not good which I don't really understand. He trained really well coming in here. I'm surprised."
Parry wondered why Phelps chose to race the 400m IM in London. "That is his weakest event of all the ones he's lined up to do," said Parry. "The 200m freestyle would have been a better shout."
Will Phelps recover?
"It's frustrating, that's all I can say. It's pretty upsetting," said Phelps. "The biggest thing now is to try to look forward. I have a bunch of other races and hopefully we can finish a lot better than how we started."
After Sunday's 4x100m freestyle relay, he will compete in the 100m and 200m butterfly events before renewing acquaintance with Lochte in the 200m individual medley.
"The 200m butterfly is his strongest event," said Parry. "He needs to deliver there and I think once he gets back into that winning mentality he'll be all right.
"But other competitors are going to be looking at Phelps now and thinking this fella is not bulletproof, so let's take him on. If that happens, then he'll start to feel the pressure.
"I just hope that, in seven days' time, we aren't asking why Phelps took part in this meet and wondering why he didn't just leave with 14 gold medals after Beijing."
Lochte thinks his rival's legacy will remain intact. "I know that he gave everything that he had, but to me he is one of the greatest," he said. "Whatever happens, he will be remembered as one of the greats."
Will Lochte beat Phelps again?
The pair are scheduled to renew their rivalry in the 200m IM on Thursday.
"Lochte will be swimming the 200m backstroke final 30 minutes before the 200m IM, so that will be a bit of a leveller," said Parry.
"To be honest, I don't think Phelps has a chance without the advantage he is going to get from Lochte swimming in the 200m backstroke.
"I am excited to see how the race will go. I hope Phelps wins and can go on to claim a couple of golds."