The Daniel Muscutt-ridden Dubai Mile was quickly to the fore in the British Stallion Studs EBF Restricted Novice Stakes and while Super Mo was a brief threat, the market leader really strode on through the final furlong to win in style.
Johnston, based at Middleham in North Yorkshire, was responsible for 4,874 winners under his own name and now shares the licence with his son, Charlie.
Born in Glasgow in October 1959, Johnston - Britain's winning-most trainer - began his career in Lincolnshire, where he set up his first yard with his wife and assistant, Deirdre.
He became the first Flat trainer to record over 200 winners in a season (2009), a feat he has repeated every year since, bar 2011, 2016 and 2020, with the latter heavily restricted due to Covid-19.
The qualified vet has won the 1000 Guineas with Attraction (2004), the 2000 Guineas with Mister Baileys (1994) and has shown a great affinity with stayers - winning the Gold Cup at Ascot four times through Royal Rebel (twice), the hugely-popular Double Trigger and most recently Subjectivist (2021).
He was also responsible for the brilliant Shamardal in his juvenile season, winning the Dewhurst Stakes in 2004.
Numerically his best year came in 2019 when he trained 249 winners, and in 2018 Frankie Dettori partnered his record-breaking 4,194th winner at York, bettering the mark set by Richard Hannon senior.
"It's obviously a bit different from breaking the record in 2018, you could say no one has reached 4,194 winners (the previous record) so it's not as if I'm breaking new ground, it's just another landmark and setting the bar higher for people to try to reach," Johnston told Great British Racing.
"The main thing is the whole business revolves around winners and a lot of winners means a lot of happy owners. Hopefully we can continue doing the same thing."
On being the joint-licence holder, he said: "There are disagreements, as there would be with anyone working with another family member!
"However, it's certainly lifted a lot of the load from me and the most important thing is he's now getting credit for something that he's been doing for quite some time in the business. That's certainly part of the plan that he will take over at some stage in the relatively near future.
"We don't know when that will be!"