Willis, 29, has earned the benefit of the doubt.
New Zealand's finest middle distance since the days of Walker, Dixon and Quax, he has defied accepted wisdom that North Africans and those born in the Rift Valley cannot be beaten when winning silver (promoted from bronze after Rashid Ramzi was caught doping) at Beijing and Commonwealth Games gold in Australia two years earlier. Far from being beyond his peak, Willis keeps getting better, smashing his national record over 1500m, running 3m 30.35s in Monaco on the eve of the Games.
Here's the rub: Willis doesn't even think that performance is particularly relevant.
Olympic running is different from Grand Prix races and he aims to prove that. Finals rarely match the times of the day and tend to be cagey, tactical affairs. Willis would back his nous against anyone in the field.
To those who think the 1500m will be a show staged for the benefit of Beijing winner Asbel Kiprop and his compatriot Silas Kiplagat, he has a message.
"I have beaten them both before. They have succumbed to terrible tactics before and I have had incredible races before.
"Kenyan runners can sometimes have a deceptive unbeatability about them because it seems like there's always a Kenyan winning."
It's all a matter of numbers, though.
"When there's eight or nine of them in a race, two or three of them are always going to do well," he said.
"In the Olympics there are only three of them and the odds of 100 per cent of them doing well are against them.
"It doesn't mean it won't happen but I like my odds if they try to push the pace without the aid of a pacemaker. It's going to be a challenge for them."
What Willis wants to see when he draws his curtain on race-day morning is typical London weather this summer - rainy and cold. If the temperature does not rise out of the teens, he said, it would be "an interesting three days".
Willis has trained with the final, next Wednesday morning, in mind. Following his record-setting performance in Monaco last month, he put off doing any more speed work until just over a week before tomorrow's heat. His first speed session then involved a 600m split that he wanted to do in 1m 16s.
"It went very, very roughly. I did two seconds slower than that. It was ugly. There are physiological benefits to that. My body is getting up to speed in time for the final."
The competition format sees Willis race in heat three tomorrow. The six fastest in each of the three heats, and the next six fastest from any heat, qualify for the semifinals. Only Nixon Chepseba from, you guessed it, Kenya, has run faster than Willis this season, so it is close to unthinkable that he wouldn't progress.
The semifinals are on Monday morning.
Although he lives in Ann Arbor, Michigan, Willis is a very proud New Zealander.
Carrying the flag into the stadium meant an awful lot to him.
You get the feeling he wants to do something special at the Games because, over 1500m anyway, it's unlikely he'll get another chance.
