The leading jockey was in the privileged position of being able to choose between the well-touted Nicky Henderson-trained grey and his high-class stablemate Mister Fisher for a race traditionally won by future champions.
Angels Breath won the Kennel Gate at Ascot on his hurdling debut before being turned over at odds-on in the Dovecote at Kempton.
Mister Fisher was narrowly beaten on his first start over obstacles at Newbury, but has since impressed at Kempton on Boxing Day and in a Grade Two at Haydock.
De Boinville insists choosing between the two was a tough decision.
“I imagine it was a closer call than many will have thought, but I have decided to ride Angels Breath in the Supreme,” he said.
“I have an awful lot of time for Mister Fisher, and he has always shown us plenty at home.
“Crucially he has translated that gallops ability to the track this season with a victory over last weekend’s Grade Two Kelso winner Rouge Vif at Kempton followed by such a success of his own when seeing off Bright Forecast in the Rossington Main at Haydock.
“I clearly know the runner-up very well, and he is Ballymore-bound, so it wouldn’t surprise me in the slightest were Mister Fisher to run a huge race in the Festival opener.
“But I feel I am right to keep the faith in Angels Breath, not that I thought he lost anything in defeat in the Dovecote, bar the winning prize on the day.”
De Boinville also had a decision to make in the Champion Hurdle and has sided with International Hurdle winner Brain Power over Verdana Blue – who inflicted a shock defeat on stable companion and dual Champion Hurdle hero Buveur D’Air in the Christmas Hurdle at Kempton on Boxing Day.
“There is very little between him (Brain Power) and Verdana Blue in terms of talent, but the probability of soft ground – or at least on the soft side – on Tuesday has just swayed me,” said the rider.
“If they don’t get much more rain though I could be having second thoughts.”
The jockey is already blessed to have won a Gold Cup on Coneygree before partnering Sprinter Sacre to Champion Chase glory in one of the great Cheltenham comebacks.
De Boinville then won a second Champion Chase on Altior last year – and the 2018 winner heads a 12-strong field for next Wednesday’s renewal of jump racing’s most prestigious two-mile chase.
The nine-year-old is looking for a fourth straight Festival success in all, having also won the 2016 Supreme Novices’ Hurdle and also the 2017 Arkle Trophy at Cheltenham.
Altior’s biggest threats appear to be trained by Willie Mullins in the form of Min, Footpad and Un De Sceaux.
Tom George is set to saddle the admirable veteran God’s Own, Harry Fry has left in Hell’s Kitchen, Paul Nicholls is not ruling out running Politologue and Harry Whittington is represented by stable star Saint Calvados.
The Alan King-trained Sceau Royal, and North Yorkshire trainer Phil Kirby’s high-class mare Lady Buttons, complete the possibles.
Joseph O’Brien has revealed JCB Triumph Hurdle favourite Sir Erec has suffered a minor setback, but is still expected to be fit for the Cheltenham Festival.
A high-class performer on the Flat, the Camelot colt has won each of his two starts over hurdles at Leopardstown this season – most recently dominating his rivals in the Grade One Spring Juvenile Hurdle last month.
He is a best priced even-money favourite for the juvenile championship next Friday, and O’Brien remains optimistic he will take his place in the field despite revealing on Twitter his charge had picked up a stone bruise.
O’Brien posted: “Just to keep everyone in the loop, Sir Erec was found to have a stone bruise...we are confident that will be more than enough time for him to fully recover and get to the race in top form.”
Jockey Joe Colliver has been charged with drink driving and is due to appear before magistrates in Harrogate next Thursday, the day that the 27-year-old is due to partner Middleham trainer Jedd O’Keeffe’s Sam Spinner in the Stayers’ Hurdle at Cheltenham.
The horse provided Sheffield-born Colliver with the biggest won of his career when landing the Grade One Long Walk Hurdle at Ascot in 2017.