Johnson and Moses identified the key factors that Gay needs to execute to give himself a chance of taking Bolt's crown and staving off the challenge from a series of contenders including Yohan Blake, Asafa Powell, Justin Gatlin and Ryan Bailey.
Bolt's explosive speed created one of the greatest moments in Games history in Beijing four years ago when he scorched the track at the Bird's Nest stadium in a remarkable time of 9.69 seconds despite slowing down toward the finishing line.
Gay, who is seeking his first Olympic medal, missed that meet with an injury and is content to have slipped under the radar leading into London. Much of the attention naturally has centered on Bolt and his rivalry with Jamaican teammate Blake.
"I am expecting a strong challenge from the United States," said Moses, a two-time Olympic gold medalist in the 400-meter hurdles. "Justin Gatlin is running well enough to win a medal, but I think Tyson Gay is going to be the one to watch. He is capable of making a tremendous start, has very good acceleration, beautiful technique and smooth transitions of speed. He is good enough to win.
"The only way to beat Bolt is to get way out in front of him from the blocks. If he does get a good start, that's trouble for everyone because it will allow him to unwind more quickly. If Gay wants to beat him, he has to get out even quicker."
[ Related: Usain Bolt has a bizarre pre-race ritual ]
Gay was solid in his heat on Saturday, running a controlled race of 10.08 into a considerable headwind. Bailey was the fastest qualifier at 9.88, Gatlin produced an impressive 9.97 and Blake looked relaxed and dangerous in running 10 seconds flat.
As for Bolt, he made a sluggish start, but responded quickly and jogged the last quarter of the race to record 10.09. No one is taking him lightly, and the world anticipates more sporting brilliance on Sunday night.
But Johnson, the 200 and 400 meter icon, is not so certain Bolt will repeat as Olympic champion.
"[Bolt] is the man from Beijing and we all know what he can do. But can he be beaten? Sure," Johnson said. "But it needs certain things to happen and if he is at his best, it will be difficult to see him getting beaten.
"But if he is just a little bit off, then Gay and some others have a chance. Most important, they need to believe. You don't want to lose the race on the starting blocks. So much of it is mental and I think if Gay sees himself as a potential champion, then he is going to run very fast."