I've seen a record 26-trick swing on opening lead, but still, 20 is a lot. Furthermore, this deal swung the quarterfinal match in the 2012 World Championships between USA and Sweden:

Late in the match (the final segment), the USA pair in the Closed Room played 5X by West down one (looking at all the cards, it can be made). But, the action was in the Open Room:

Vul: East-West Dir: North	4 10 6 K Q 8 5 4 3 2 A 6 2
A K 10 8 7 5 3 K 9 3 2 -- 8 3		6 2 A Q 5 J 9 6 Q J 10 9 7
	Q J 9 J 8 7 4 A 10 7 K 5 4

Here was the aggressive auction by North-South:

West	North	East	South
	3	Pass	3NT
4	4NT	Dbl	All Pass

All would have been well had West led 4th from his longest and strongest. Declarer would have won the spade lead and claimed 10 tricks and his contract.

West actually led a low heart at trick one. Perhaps East should try the queen (which would later make things easier for his partner), but he won the ace. He returned a spade to the jack and king and West was at the crossroads.

He could cash out for down one (ace-king in both majors). That's what everyone watching thought (I was one of the broadcasters on BBO). We all got a shock when West went "all in." Instead of cashing out, he laid down the K and did not take his high spade. He risked another heart. He crossed to partner's Q for another spade which now meant down 7. The defense took the first 10 tricks for +1700 and won 18 IMPs on the deal. They held on to win the match by 4 and went on to win the World Championship.