Because they believe Hands Christian has a better draw, more consistent manners and more improvement in him.
Hands Christian has had only two starts back from an injury-enforced break that saw him not race for 28 months but both those runs have been brave.
He was fourth fresh up behind Terror To Love and then led and was caught late by Adore Me at Ashburton.
"And you would think he will improve with those runs," says Purdon.
"We are thrilled with how he has come back up after so long off and he has been strong to the line in both his races. His manners are good, too, and I can see him being handy to the speed, maybe even leading if Christen Me doesn't.
"And that would make him hard to beat because Nat was thrilled with him in the Cup trial last Wednesday. She thinks she could have won that had she got serious."
Hands Christian has always been a serious horse and also boasts an Easter Cup win over Terror To Love, beating him, Gold Ace and subsequent Hunter Cup winner Mah Sish in the 2012 Easter Cup, after settling behind all three.
So all of those factors add up for Purdon to rate him ahead of Adore Me, even though she is one of our great modern mares. Her Ashburton win was comprehensive but came courtesy of a brilliant standing start beginning which gave her a huge tactical advantage.
But her chances of settling handy tomorrow diminished enormously after two separate events last Wednesday - she drew the second line and then galloped away in the Cup trial.
"We are hoping being off the second line helps her begin better and concentrate because she went great in the Cup trial after that," says Purdon.
"But even if she begins well it is hard to see her getting in front of the other favourites and that means she could need a lot of luck, whereas they might not need as much.
"So while she can win Hands Christian has to be our best chance. I'll be honest, her gallop in the Cup trial did knock my confidence just a touch."
Purdon, who also has Arden Rooney as an outside place hope tomorrow, is looking for his first New Zealand Cup win since Il Vicolo defended his title in 1996, an incredible drought considering how many headline pacers he has trained since.
He has had a placegetter in the last four Cups, with Fly Like An Eagle, Highview Tommy (twice), Sushi Sushi and Sleepy Tripp, with his two big names tomorrow better horses than any of that quartet.
The Purdon-Rasmussen stable also have five starters in tomorrow's $170,000 Sires' Stakes and rate Alta Orlando as their best chance, even though the gawky pacer starts from the unruly.
"I think there is a chance they will go hard early and then he can come into the race so being unruly might not be a bad thing," said Purdon.
"But Hughie Green will be hard to beat.
"He is staying at our place and has settled in well and is a lovely horse so we know what we are up against with him."
While the leading stable has huge representation tomorrow, their best winning hopes come in the support races.
Purdon opts for Backup (race two) and Rare Opportunity (race three) as two of their better chances and perhaps surprisingly Messini over last season's Cup runner-up Fly Like An Eagle in the free-for-all.
