Champoussin was part of an earlier breakaway that was caught but he fought back on the last climb to reconnect with a select group of GC favourites, that had slowed in a game of cat and mouse, before he launched an astonishing late-race attack and crossed the line with a solo win.
He finished six seconds ahead of overall leader Primož Roglič (Jumbo-Visma) and eight seconds ahead of Adam Yates (Ineos Grenadiers) at Mos. Castro de Herville.
Roglič retained his overall race lead with an advantage of 2:38 over Enric Mas (Movistar) and 4:48 over Jack Haig (Bahrain Victorious), who moved up to the podium spot after Miguel Angel Lopez (Movistar) missed a decisive split 55 kilometres from the finish and then abandoned the race.
Watch the race highlights above to see how stage 20 unfolded at the Vuelta a España.
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