Michael Phelps has claimed the 21st gold medal of his career, anchoring the United States to a dominating victory in the 4x200-meter freestyle relay.

About an hour after winning gold medal No. 20 in the 200 butterfly, Phelps completed his grueling double with a triumphant four laps of the pool.

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The result was no longer in doubt by the time Phelps dove in. Conor Dwyer, Townley Haas and Ryan Lochte made sure of that, handing off a commanding lead to the most decorated athlete in Olympic history.

Phelps essentially spent the next 100 seconds or so on a victory lap, the crowd’s cheers growing louder with each stroke. He touched in 7 minutes, 0.66 seconds, a full body length ahead of Britain’s James Guy.

The British earned silver in 7:03.13, while Japan took the bronze in 7:03.50.

When it was done, Phelps simply sat on the starting block, thoroughly exhausted. He motioned at his neck as though he had nothing left to give.