The GIG: Analysing Pouille & Wozniacki’s win probabilities

Win probabilities are notoriously hard to forecast. Take Lucas Pouille, for instance. Midway through the fifth set of his match against Rafa Nadal he had a win probability of just 5%. How was it calculated? Stephanie Kovalchik from Tennis Australia’s Game Insight Group (GIG) analysed a number of fourth round matches from Day 7 of the US Open, determining the key moments where the momentum ebbed and flowed due to a player’s ELO Rating.

To read analysis of other matches, visit on-the-t.com.

Pouille shocks Nadal

The most unlikely win of the fourth round had to be Lucas Pouille’s victory over an in-form Rafael Nadal. The forecast for Pouille’s chances of overcoming the Spaniard were just 14%. It was going to take a strong lead to overcome that deficit. Pouille sent out the message that he wasn’t going to take his ticket home easily when he won the first set at 6-1. Still, even the set on the board only increased his chances to 30%.

The odds went against him again when Nadal took the second, but Pouille found a way to win the third. The major turning points in the third set were the early break Pouille won in the first game, and fighting off break points on his serve in the fourth game.

Fascinatingly enough, even with two sets secured Pouille was still below 50% for the win – Nadal remaining the strong favourite on serve and return.

Pouille appeared to be losing belief, starting with the break point in the fourth game of the fourth set and the eventual break of his serve in the sixth game. Things got really rocky from that point on as Pouille lost the fourth set and was broken immediately in his first service game of the deciding set. By the seventh game of that fifth set, Pouille’s odds of pulling out an upset had hit a low of 5%. With the end of the set approaching, Pouille somehow worked a mental miracle in the eighth game by winning a break back. That would turn out to leave it all to the tiebreak.

Even at that point, the probability calculations didn’t believe that Pouille could do it. After losing the first point, Pouille had to win 4 points straight to get the stats on his side. At that point, he was a 50% favourite and he, in one of the most impressive battles of the Open, fought to hold on to that advantage and take the win.

Wozniacki in cruise control

With the losses and injury struggles Caroline Wozniacki has dealt with this season, she was the low-probability bet going into her fourth round match against American Madison Keys. FiveThiryEight predictions gave Wozniacki only a 33% chance of taking the match. The Dane appeared to have no interest in what these numbers had to say, though, when she got the first break in the fourth game of the first set. That achievement put the odds at an even draw.

Wozniacki continued to add to the pressure on Keys in the sixth game, creating two more break chances. Wozniacki didn’t convert, however, but she didn’t need to. Both players held serve for the remainder of the set, giving Wozniacki the first set.

With the first set in the bag, Wozniacki went into the second set with a 70% chance of taking the match. That rose to 80% when she earned a break in the first game. Keys threatened a comeback in the fourth game when she got the break back, only to broken in the next game. At that point, Wozniacki’s win probability was at 90% and her spot in the quaterfinal secured.

This article first appeared in on-the-t.com.