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.

At 4-4 in the third set, Zverev was surging hard after winning 11 of the previous 15 points to erase a 1-4 deficit. Sock had won 17 of the first 22 points of the third set, so nobody really knew how this was going to finish.

At 4-4, Zverev’s ‘A-Game’ game struggled - and Sock needs to take all the credit for that.

“I choked. It's quite easy,” said Zverev, afterwards. “I won the second set 6-1. I was 1-0 with a break. He got a point penalty. I was down 1-4 within 10 minutes where I didn't put many balls in the court,” Zverev said. “So, yeah, I just choked.”

Fast forward to 4-4 in the third set and you can see by the patterns of play that the flow and control of points, whether won or lost, were played much more on Sock’s ‘first strike’ preferred terms of engagement.

Serving at 4-4, on the first point, Sock directed his second serve to Zverev’s forehand, and the return went straight into the net. The door just cracked open a little for the American. Sock double faulted, then at 15/15 he hit a Serve +1 forehand approach winner off a short forehand return. Sock won the next point with a drop shot, and closed out the game with a serve and volley point to Zverev’s forehand.

No rhythm for Zverev. No backhands for Zverev. No oxygen for his game at The O2.

With Zverev serving at 4-5, Sock missed a forehand return on the opening point. If he was going to lose a point at this stage of the match, it was actually better to do it this way than let Zverev feel comfort and consistency with his groundstrokes. On the next point, Sock approached with a Return +1 forehand and finished with an overhead.

The 4-5, 15/15 point provided a perfect snapshot of the tense nature of Zverev’s game. Sock hit a forehand return, then directed his backhand down the line trying to find Zverev’s forehand. The tall German moved to his right to hit a backhand standing in the Deuce court to protect his mis-firing forehand. Sock went straight back down the line and found Zverev’s forehand on the next shot, and it sprayed wide.

Sock’s strategy had nothing to do with his side of the net. It was simply to hunt down Zverev’s forehand.

You can definitely connect the dots with the double fault at 30/30, and the forehand Zverev missed on the previous point, and the one he missed on match point that was pushed wide down the line.

Zverev would finish with six forehand winners and 18 forehand unforced errors for the match. Overall, Zverev hit 140 backhands and just 79 forehands. It becomes very difficult to win a match on this stage without the forehand being a dominant force. In the third set, Zverev hit 62 backhands and just 39 forehands.

Zverev’s court position also told a story of the defensive nature of his mindset. Zverev made contact with 39 per cent of his ground strokes more than two metres behind the baseline. Sock was only back there 23 per cent of the time.

We all see Sock’s serve and forehand are his big weapons, but his ability to dissect an opponent and break down their strengths deserves just as much recognition.