The former Mayo forward acclaimed the commitment of Donegal’s players to the system devised by Jim McGuinness which he felt gave them a blueprint for victory over the reigning champions.

In particular, the training camp Donegal went into at Johnstown House in Enfield, Co Meath during the week allowed McGuinness and his players time to create and practice the tactics that proved hugely successful on the day, McStay said.

“When I heard they were gone away for five days to Johnstown [House] and knowing the sort of detail and the work that they go into, you [would’ve] had to fear that Dublin were going to get the most severe test that they got this season and ultimately that’s probably the reason Dublin were beaten, they hadn’t been road-tested,” McStay said on RTÉ’s ‘The Sunday Game’.

“Donegal came in so well prepared, so focused and so confident about the system that they absolutely believe in, which of course was conjured up by – he’s almost spiritual at this stage – Jim McGuinness; conjured up by him and a total acceptance of the demands of that system by all his warriors and they turned the tables

“It’s the biggest shock, I’d say, in the last ten years of football. [Dublin were] 10-1 on, on Friday when we spoke and they beat them comprehensively,” he added.

His fellow pundits Marc Ó Sé and Mark McHugh – who left the Donegal panel six weeks before the start of this year’s Ulster championship – agreed with the Mayoman’s views on the game.

Kerry legend Ó Sé identified the periods both sides of half time as crucial to Donegal’s victory and warned that Donegal would seriously worry his native county in the run-up to the final in three weeks’ time.

“They were brilliant,” Ó Sé said, “I thought the last ten minutes of the first half and the first 15 minutes of the second half, they were absolutely outstanding and when they get that couple of goals it’s really hard to catch them; they defend really, really well – they have the best defensive system in the country and everybody has a role.”

McHugh, brother of man-of-the-match Ryan McHugh, said he believed Dublin’s tactics of pushing their half-backline forward proved costly and played into Donegal’s hands.

“I felt if we look at Dublin’s last number of years when they’re really playing well, they played with their zonal defence [but] they followed Donegal’s half-forwards up the field today which left a gap for the runners coming through and it really played into Donegal’s hands especially in the second half – you’d Frank McGlynn; Ryan [McHugh] coming through; Karl Lacey; Michael Murphy and there was just no stopping them,” he said.

McHugh also said that while he found it difficult to watch the team he left earlier in the year progress to an All-Ireland final, he had no regrets over his decision which he explained he felt was best for him at the time and added that he was delighted for the panel of players and his younger brother in particular.