He came into the Olympics in London having lost recent showdowns with a rival from his own country. Though he was magnificent in Beijing, the word was that he had slipped from his top form and could be beaten in London.
Usain Bolt, track and field? Michael Phelps, swimming?
Phelps showed signs of slipping in last year's World Championships, where Ryan Lochte beat him in the 200-meter freestyle and the 200-meter individual medley, continuing a trend of Lochte getting good results head-to-head with Phelps.
Bolt also gave up a world title last year, though it was decided on a false start in the 100-meter dash. Yohan Blake took that title, then beat Bolt twice head-to-head in the Jamaican trials. A rivalry was born. And, coming into the Olympics, Blake had a faster time in the 100-meter dash.
In London, Phelps once again proved to be the best overall swimmer in the world. Yes, he finished fourth in the 400-meter individual medley and botched the finish in the 200-meter butterfly. But, he got better as the meet went on. Those four gold medals and head-to-head win over Lochte don't lie.
A few days later, Bolt stepped up for one of the greatest moments of truth in sports—the 100-meter dash final. Then, 9.63 seconds later, Bolt was clearly a step ahead of the pack.
Bolt still has more racing to go. Blake will challenge him again in the 200-meter dash, and then they'll team up for a relay in which they'll be heavily favored.
Who has had the most dominant career?
But, the title "World's Fastest Man" is traditionally reserved for the man who does it in the straightaway in the 100-meter dash. Check the all-time list for the fastest times ever, and the only man who has ever gone faster than Bolt did in London is Usain Bolt, in the 2009 World Championships.
Both athletes have shown that their Beijing dominance can't be taken for granted. The time between each Olympic Games is long.
That's why feats such as Phelps' three-peats are so rare. And it's why Bolt is the first man to win back-to-back gold in the Games' marquee sprint since Carl Lewis.
Phelps didn't win quite as many gold medals in London as he did in Athens or Beijing. Bolt may be ever so slightly slower today compared to his times from the last decade.
Yet, each man was so far ahead of the rest and so dominant in his sport that he could afford to slide from his peak and still be, unquestionably, the best.
Beau Dure worked with USA Today to cover six Olympic Games from 2000 to 2010, traveling to Salt Lake in 2002 and the last three in Torino, Beijing and Vancouver. He tracks Olympic sports and other sports on Twitter (@duresport) and on his blog, SportsMyriad.com