10/08/2016 11:59 AM AEST | Updated 11/08/2016 2:05 PM AEST

Michael Phelps Won His 20th Olympic Gold Medal. Then He Won His 21st.

And #20 might have been the greatest one yet.

Michael Dalder / Reuters
The greatest.

RIO DE JANEIRO -- The weirdest thing happened just before Michael Phelps won his 20th Olympic gold medal in the 200m butterfly at the Rio Olympics.

Just before the start of the race, the eight swimmers were called off their blocks because of noise in the crowd. This has been a persistent problem here at the swimming in Rio. But that's not the weird thing. The weird thing is what happened next.

After the swimmers had hopped off their blocks and stepped back up, the crowd was properly hushed for once. There was one sound in the entire stadium and one sound only. It was the sound of Phelps slapping his giant chest with his enormous arms. You could hear it all the way from down at the pool deck, way up to row ZZ.

It was the sound of a predator.

We've seen Phelps in focused mode this week, headphones on, stony stare, calmly plotting the demise of his rivals. This was different. This was Phelps the beast. This was Phelps who had been chased down and beaten by a Hungarian in the semi-final of this event a night earlier, but who was determined to extract every last ounce of animal from his 31-year-old purple-spotted frame.

He did, too.

Phelps led the whole way. Just when you thought the others were coming, they weren't. When you thought they were coming again, they still weren't. When you really thought OK, this time they're actually chasing him, you slapped yourself as he had slapped his own chest and said no, they're not coming. Because he is Michael Phelps and they are not. He's got 20 Olympic gold medals and they've got pocket change.

(Update: Apparently 20 wasn't enough. Phelps then turned right back and bagged #21. There's no stopping this guy.)

Michael Dalder / Reuters
Part man, part sea monster.

He's the greatest swimmer of all time, and they're the guys in the pool alongside him who were there when it happened. Ordinarily that would be a disrespectful thing to say to some of the world's best credentialed swimmers, but not on this night. Wow.

Michael Phelps came to the 2016 Rio Olympics with five events on his program. He won his first, the 4x100m freestyle relay, recording a sizzling time in his split which made you wish he'd put the individual 100m on his program.

And now he's crushed the word in the 200m butterfly. He won by just 0.04 of a second yet it was somehow never in doubt. The time of 1:53:36 was nearly two seconds outside his own world record set in 2009, but so what? The Olympics are about drama, not statistics. This was the most amazing thing to watch.

For the record, Japan's Masato Sakai took the silver, with bronze going to Tamas Kenderesi of Hungary. But this was all about the greatest there's ever been. He knew it too. After the race, Phelps stood calmly in the water, finger held aloft as if to say "who's number one?".

Like anyone needed reminding.

Marcos Brindicci / Reuters
He knows it, we know it.

Phelps was amazingly calm in this moment. He was not the alligator wildly thrashing around that he'd been just moments earlier. He was the 'gator that had just feasted on its prey, calm, awesome, frightening in its power.

The feast's probably not over yet at these Games for Michael Phelps.

And in the post-race glow, the cameras turned to his adorable baby boy Boomer, cradled by his fiancee Nicole Johnson. And then Phelps shed a tear on the medal podium. And suddenly the beast was a softie again.

For now.

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