On Sunday, the trainer and jockey combination produced Hernando to take the Prix du Jockey-Club (French Derby) to add to their successes with Kingmambo and Madeleine's Dream in the Poule d'Essai des Poulains and Poule d'Essai des Pouliches (French 2,000 and 1,000 Guineas).
Their dizzy start to the season is a poignant one, not least because Boutin is suffering from a serious illness, but also because it marks something of a homecoming for Asmussen.
When he arrived in France 11 years ago as a 20-year-old American jockey with a prolific record at the East Coast tracks, it was to take up a contract to ride for Stavros Niarchos, the owner of Hernando and Kingmambo, the majority of whose horses are trained by Boutin.
After an opening four-year spell riding for Niarchos, Asmussen has subsequently linked up with Mahmoud Fustok, Vincent O'Brien, Barry Hills, and Andre Fabre, as well as riding as a freelance for the last two years. During that time he has ridden horses of the calibre of Suave Dancer, Last Tycoon, Golden Opinion and Soviet Star.
His best horses have been French-trained, seemingly instant vindication of the view that his spells with O'Brien in Ireland and Hills at Manton were more ignominious than glorious.
Asmussen, however, argues: 'Some people like to say I've only succeeded on the French tracks, but that's inevitable. I mean I've only spent 11 years of my life doing that, improving my skills here. If I spent the same amount of time in England and Ireland, I'd like to think the results would be the same.'
The decision of Freddie Head to ride freelance himself this season has brought Asmussen full circle: back to Boutin and Niarchos. It is, he says, 'like renewing an old love affair, it's very special.'
As his first name, coined by his father and legally changed in 1977, would suggest, Asmussen is a businessman as well as an undeniably talented jockey. So when he opens the door to sentiment, you know it's for real.
Describing the successes of this year, he stresses: 'I know there is a personal feeling in this. Mr Niarchos was the man who brought me here 11 years ago, and he took a big risk.
'There's so much communication going on between us (himself, Boutin, and the Niarchos camp). Now we can say in two words what might have taken an hour before.
'Also, Francois hasn't been able to go racing very much this season, but I look forward to coming back from the races and talking to him about everything. I know the kind of things he's looking for so I can go back with the information, he can put it into the (metaphorical) computer and run the print-out.'
Such eloquence is an Asmussen trademark. He often injects phrases into his conversation which would be the envy of a political spin doctor.
His career out of the saddle, talking to trainers, owners, whoever, is a case of 'laying the groundwork for tomorrow'. It's a motif to delight any party leader.
And in reply to suggestions that he had been unaware of the true capabilities of Hernando (unraced at two) and Kingmambo, seemingly the confirmed inferior to Zafonic, Asmussen says: 'That is opinion, that is what the races are for - to disprove opinions and make results.'
He hopes to produce the right result next Tuesday when Kingmambo, the only horse to have beaten Zafonic, takes on that mighty colt again in the St James's Palace Stakes at Royal Ascot.
'Kingmambo is a horse that is very much improving,' Asmussen says. 'People said when he beat Zafonic in the Djebel (at Maisons-Laffitte, the three-year-old debut for both colts) that Zafonic ran below form. But Kingmambo improved about 7lb after that race.
'I don't know if Boutin is specifically targeting Zafonic, but I do know he's awful happy about his horse.'
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