Thomas, Mark Richardson and Jamie Baulch formed a block booking after coming safely through their semi-finals, However, Thomas, who was being thought of as a potential champion here before Michael Johnson's arrival on a wild card, walked heavily away after finishing fourth, and spent much time frowning and stretching before leaving without comment.
Britain's record holder has been complaining for several days of a niggling injury behind his right knee. Having said that, he ran 44.61sec, which made him the fastest Briton. His race was won by Johnson, who quelled some of the doubts that his previous day's absent-minded performance had raised by running 44.37 with apparent ease.
Richardson was second behind another American, Tyree Washington, in 44.62, with Baulch third in 44.69. Like Thomas, Richardson is troubled by a knee injury, but it is clearly not affecting him.
"I've got to be pleased with a season's best slowing down," Richardson said. "It's a job well done. I wanted to get into the top two so I can get a middle lane in the final. It's super stuff to have all three of us there."
He paid tribute to his trainer, Mark Zambada, who has been working on his leg. "I wouldn't be running here if it wasn't for him," Richardson said. "He's an amazing guy. "I'm not letting the injury affect me. If it's going to go, it's going to go."
Baulch, who as far as anyone knows is not suffering either illness or injury, spoke to his coach, Linford Christie, afterwards. "I didn't really go for it in the first 200," he said. "I was just telling myself 'You are The Man.'"
Today will tell. But the man whom most expect to be The Man, Johnson, provided a more reassuring show.
He neither looks nor acts like the man who won two golds in Atlanta. The injury he suffered in his challenge with Donovan Bailey at the end of May still appears to be having a knock-on effect. There is a chink of light for the Brits, then. But Johnson does not look as if he will need his best to retain his title.