"To make a putt like that, it's a dream come true", the 33-year-old told europeantour.com.
Fox's consolation was a tee-time into The Open and with Nuneaton's Andy Sullivan (69) and South African Zander Lombard (69) securing the other two Carnoustie places.
Campillo may have managed the lowest score on Sunday, but the performance of the day surely came from Jon Rahm, who managed a six-under 66 - rounded off with four birdies in succession - despite registering a triple-bogey seven on the second.
The victory earned Knox a prize of nearly £890,000 and his first win since the Travelers Championship in the United States in 2016 as he moves up to fifth place in the Race to Dubai standings. He'd already marked our cards with back-to-back T4s in the Scottish and Irish Opens past year but this acts as a further reminder that he's a go-to guy whenever the European Tour heads for the links. He will now head to Carnoustie full of confidence and has thrown his hat in the ring for a place in Europe's Ryder Cup team. To make the Ryder Cup team you have to win tournaments.
The result will also go a long way to guraranteeing Fox his European Tour card.
Fox birdied the 12th and put his third to three feet on the par five 13th to lead by two but he bogeyed the next, with Knox joining him at the top after a tap-in at the 15th.
After Knox made birdie on No. 18 to set the clubhouse target at 14-under par, Ryan Fox of New Zealand missed an 8-foot (2.4 metres) birdie putt that would have won him the Rolex Series event.
A pitch to 10 feet gave Fox his opportunity but the putt slid by to ensure the play-off.
In terms of the Irish on the field, Rory McIlroy and Shane Lowry were best placed, both on 2 under, 12 shots off the victor.
As for McIlroy, he left Ballyliffin feeling better about his putting after getting an overnight message from his putting whisperer Brad Faxon on his body language. 'I got to 18th in the world and I saw how good the players were around me. "It seemed to help out there today".
Knox closed the tournament with a magnificent round of 66 at the fabulous Ballyliffin Golf Club (Watch Course VLOG), which turned out to be a wonderful venue.
Sunday's crowd figure of 27,055 brought up the week's tally to 94,239 - nearly 2,000 more than attended last year's event at Portstewart.