Shinkwin had looked set for his maiden European Tour title and the first prize of £898,000, only to fluff his chip to the 18th in regulation and then leave a putt to win the £5.4million event short from just four feet.
The pair returned to the 18th for sudden death and Cabrera Bello, whose closing 64 had set a new course record at Dundonald Links, produced a stunning approach to the par five to set up a two-putt birdie.
Shinkwin's approach had finished in an almost identical place as it had on the 72nd hole and after pitching over a bunker to seven feet, the 24-year-old again hit a tentative putt which came up short.
Cabrera Bello had started the day four shots off the lead and despite going to the turn in 32, was unable to gain much ground as Shinkwin followed six straight pars with a hat-trick of birdies from the seventh.
Further birdies on the 13th and 15th kept Shinkwin out in front, but Cabrera Bello kept up the pressure by picking up shots on the 12th, 14th and 17th before enjoying a slice of luck on the last as his approach hit the right-hand side of the burn which guards the green and bounced over to the other side.
From there the 33-year-old chipped to three feet for a closing birdie and that proved enough for a playoff after Shinkwin dropped his only shot of the day on the last.
The former English Amateur champion, whose caddie Andy Sutton worked for Ben Curtis when the American was a shock winner of the 2003 Open, at least had the consolation of a place at Royal Birkdale and a cheque for £598,000.
France's Matthieu Pavon also secured a major debut at Birkdale with a closing 66 to finish third on 10 under, with Australia's Andrew Dodt claiming the last place ahead of England's Anthony Wall by virtue of his higher world ranking.
Ian Poulter, who began the day in a tie for the lead in pursuit of his first win since 2012, could only manage a closing 74 to finish in a tie for ninth.