Your number one job in a match is not to play great. It’s to make the opponent play bad. Jack Sock defeated Alexander Zverev 6-4, 1-6, 6-4 on Thursday evening at the Nitto ATP Finals by doing exactly that. Sock didn’t play amazing tennis, but that’s not really the point. Sock didn’t beat himself, which has much more to do with why he has successfully navigated his way through to the semi-finals this weekend.