US Open 2018: Del Potro can challenge "resurgent" Big Three

Del Potro US Open
Del Potro can eye victory on the stage that brought his sole grand-slam win
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Listening to some previewers you'd be forgiven for thinking that the Big Three are back in charge, writes Jack Houghton, but the numbers suggest something more nuanced is happening in the men's game...

"What Elo ratings show us is that the men's game is in a stage of relative depression, with Djokovic, Nadal and Federer only able to retain their lofty positions because of a lack of competition..."

Reading and watching the various previews of the men's draw ahead of the US Open, all the talk seems to be about the re-solidifying of the Federer-Djokovic-Nadal triumvirate. We are back, it seems, in the days when a grand-slam prediction was based around which of these brilliances was likely to be slightly more brilliant than the other. Indeed, one previewer claims that there is an 80% chance that one of the Big Three takes the title home.

They certainly head the market, but not quite to that degree of dominance. With Djokovic at [3.45], Nadal at [3.90] and Federer at [7.40], punters view the trio as having a combined chance of around 68% to claim the win in New York. In other words, the market predicts that, if this tournament were to be played three times, the threesome would only add to their combined ten titles twice.

That's a big difference to the four-out-of-five claim of that previewer.

Tough draw for two of the Big Three

And it's no surprise that the market is more lukewarm about the trio's chances. First, the draw has not been kind to either Djokovic or Federer, who could meet in the quarters, but also, rather than recent months seeing a re-solidifying of the Big Three, something different is happening in the men's game, which is only evident when you look beyond the crude measures of tournament victories and ATP rankings.

Yes, it's true that the trio have shared this year's grand slams between them. And yes, they have been prominent again in the warm-up tournaments for this year's US Open, with Nadal winning in Toronto and Djokovic beating Federer in the final at Cincinnati. However, these bare facts do not tell us the full story.

Novak, Roger and Rafa all down on their peak

To have a more complete understanding of whether this season is seeing a genuine re-emergence of the Big Three at the top of the men's game, it is necessary to look at some indication of their playing form which allows a comparison to their form of yesteryear, and measures like those encapsulated by Elo or Glicko ratings enable us to do this.

And what they show - at least, what my Elo ratings show - is that the men's game is in a stage of relative depression, with Djokovic, Nadal and Federer only able to retain their lofty positions because of a lack of competition.

To better understand this, it's worth pinning some numbers to the claim. Djokovic is favourite for the US Open despite being a 300-point worse player than at his peak. To set this in context, it means that, theoretically, were current-Djokovic to play peak-Djokovic, he would only have a 15% chance of winning. In other words, he would be around a [7.00]-shot. Federer is 250 points down on his peak. Nadal is 150 points down.

So, the trio may seem to have this US Open between them according to some previews, but if they do (and they really don't), it's not because of their personal form, but because of the paucity of the challenge that they face.

As punters, of course, these historical comparisons of ratings can seem irrelevant. It can be reasonably claimed that where a player sits in comparison to their career peak does not influence their chance in individual matches or tournaments. The only thing of note, the argument continues, is how their current ratings compare to the players they will face on any given day.

This is all true to a large extent. However, it's worth remembering that ratings systems like Elo are retrospective analyses of performance and, whilst they might prove accurate predicters of chance in most match-ups, they are not well-designed to predict likely future movements in a player's rating. In other words, they tell us where a player is at right now, and not whether their rating is likely to go up or down in the future. That is, whilst Elo includes a self-adjusting mechanism to account for improvements and declines in form, it is not always responsive enough to significant change, such as an up-and-coming player showing a rapid improvement in form.

One way of playing around with these numbers, then, is to think about a player's age. Djokovic is 31, Nadal 32 and Federer 37. Looking at the Elo ratings of previous champions, it emerges that, for those who continue playing into their thirties, most drop an average of 60 Elo-points a year. This analysis is slightly crude, of course. It's based on a small sample and doesn't take account of the fact that, more recently, players seem to be aging better, with Federer the exemplar: his Elo decline past 30 is half the all-time average.

What we can suggest, though, is that it is unlikely that their Elo ratings are hiding some imminent and rapid increase. Federer's peak Elo rating was reached over a decade ago, and Nadal's not much after. It would be a surprise to see either trending back towards those peaks in the coming seasons. Djokovic's profile is slightly different. His Elo peak came as recently as 2016, and as he recovers from his woes of the last couple of years, we can perhaps expect his number to correct upwards, although it is unlikely he will ever recover that sparkling form of 2016.

All of which leaves us with a question: if this still brilliant but likely declining trio are not the sure-things they once were, who might cause an upset?

Del Potro set for a strong fortnight

For a full form guide for possibilities, check out Andy Swales' preview, but I would point you towards another aging player. Del Potro has re-emerged as a danger to the world's best in the last couple of seasons and, assuming he can dispatch returning-from-injury Andy Murray in the third round, he could upset the Big Three on the stage where he secured his sole grand-slam triumph in 2009. Del Potro has been consistent this year, and if looking at hard court results only, his Elo rating is within 50 points of the Big Three, suggesting that, in a head-to-head match-up against any of them, he would be around a [2.32]-shot. In the context of the whole draw, where Del Potro won't face either of the Big Three until the semi-finals at the earliest, his odds of [19.00] look like value.

Complicating Del Potro's quarter of the draw somewhat, though, is Stefanos Tsitsipas. If Elo ratings are significantly undervaluing any player now, it must be the 20-year-old Greek. I currently have him around 200-points inferior to the best in the world (meaning he would have only around a 25% chance of beating one of them in a head-to-head), but given his runs in Washington and Toronto and the promise he showed in those performances, it's entirely possible that his rating is still undervaluing his ability. His defeat at the hands of David Goffin in the first round in Cincinatti demonstrated, though, that rising stars tend to struggle with consistency against the best players in the world, and so I'm not tempted by Tsitsipas's odds of [75.00] for US Open glory.

The market says that if we rolled this US Open dice three times, either Djokovic, Nadal or Federer would turn up twice. If you take the view that this will happen, Dan Weston's advice to support Nadal might be the way to go. On one occasion, though, we'd get a different result, and if the dice rolls that way over the next two weeks, my money is on it being Del Potro.

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