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When the curtain lifted for the 2017-18 season, what price was another Joao Moreira magic show? The Brazilian had put up margins of 50 wins, 88 wins and 63 wins over Purton in his previous 3 seasons and even the most conservative assessor would have said that the right price about a repeat title victory was no better than 1-10, or 1.1 in decimal parlance.
Yet, here we are with 6 weeks of the season to run and not only is Purton giving Moreira a run for his money but many, including the Brazilian himself, are saying Purton is the right favourite.
How did we get here?
Purton is already just one win off his career best tally of 112 so he is ahead of where he has previously been, but Moreira has come back to him sharply.
There has been some impact felt from time out, but not in a huge way.
In 2016-17, Moreira had 4 suspensions for careless riding locally, the same as he has picked up this year, but this time around he did also come back from Melbourne with a suspension during the spring carnival as well as an injury which cost him a couple of meetings.
Purton, meanwhile, had 3 suspensions in 2016-17 and has kept it down to just two bans this season.
So there is some lean towards Purton there, just not enough to make up the wins that Moreira is missing.
Moreira has been marginally the better jockey of the pair since he landed in Hong Kong which, added to his ability to ride light and the extra opportunities thereby created, led to his runaway title wins.
But most commentators have felt Purton has had the edge in performance this term, while Moreira seems to have been simultaneously impacted by what might be called "star fatigue".
Anywhere in the world, a firmly-implanted champion jockey like Moreira - or Douglas Whyte before him - has a lot of pulling power when it comes to choice of rides.
Trainers and owners will wait for a yes or no decision on a booking for a dominant jockey, and the jockey usually makes them wait too, keeping them on the hook to make the latest, best decision he can about riding or not riding their horse.
But there is an ebb and flow to it, and, over time, some trainers start to feel hard done by and resent being hostage to a jockey's choice, which could leave them without a top rider by the time the decision is made.
Maybe that's part of it, and maybe Purton has been more proactive lobbying for his own cause this season, but there has been a clear shift of loyalties from several major stables.
Highlighted in green on these tables are the yards for which each jockey has managed a 20% or better strike rate over the last 3 seasons. What stands out is the drop-off in the number of those stables for Moreira this season compared to the past and more importantly, which stables they are.
Last season, Caspar Fownes, Danny Shum and Dennis Yip provided 37 wins for the Brazilian from 114 and 21 from 140 for Purton.
This season, the same group of trainers has provided Purton with 185 rides for 46 winners (so far), while Moreira's rides there have dried up - just 78 rides for 9 wins.
That's a swing of 81 rides and 53 winners to Purton, which suggests that the quality of those rides has probably improved as well.
(In fact, the overall profile of Purton's rides has improved this season - in the two previous seasons, his rides averaged 9.0 or better and the figure has dropped to 6.8 this term, while Moreira's average starting price has gone from 4.7 in the two previous seasons to 5.88 this season.)
It's also significant that those 3 trainers are sitting third, sixth and eighth on the trainers' championship ladder.
It's often said in Hong Kong that John Size makes the champion jockey and there is something to that, especially as, historically, Size will not help another jockey beat his main jockey in the championship.
When Whyte and Prebble were engaged in close battles a few years ago, all rides for Prebble from Size completely dried up and Whyte scraped home.
But, while Moreira has kept his powerful position with the premier yard - and Size has given Purton less support - simultaneously losing 3 strong stables to Purton looks to be making the difference that might ultimately cost him the title.