Three times towards the end of the third quarter in their Ulster semi-final with Donegal in late June, Tyrone's Martin Penrose made uncharacteristic mistakes in possession for such a composed player.
On the the first occasion, Penrose got the ball from a short kick-out and made headway down one flank until he met a wall of green and gold shirts and had to check his stride. It had been that way all evening as the most tactical battle of the summer developed.
Seeing nothing on, Penrose punted the ball infield, a tired, frustrated kick that was cut out and swept away where, just over 60 seconds later, Ryan Bradley put Donegal ahead.
Within a few minutes, Penrose was under pressure again -- this time booting out over the sideline in an overcooked pass to Colm Cavanagh.
When Neil Gallagher subsequently dispossessed him in the next passage of play, only for Joe McMahon to retrieve, Penrose had the look of a boxer on the ropes. Punch drunk.
For 50 minutes or so Tyrone had stuck diligently with Donegal. Mickey Harte had opted to play them at their own game and it was working a treat. For the only time in their six-match championship campaign, Donegal were actually behind at half-time.
But now, as the third quarter drew to a close, the squeeze was on. The Ulster champions were preparing for the 'kill.'
Death by Donegal can be a slow, grinding process, almost boa constrictor-like.
Mayo's last two All-Ireland final appearances against Kerry were effectively over after 25 minutes. The same can't happen this time because Mayo are a much smarter, street-wise side and Donegal never rush to take an opponent out straight away. They are composed and almost always in control.
Only once, against Tyrone, have they been behind by any more than one point in over 42 minutes of football.
Joe McMahon put Tyrone 0-7 to 0-5 clear just after half-time in that Ulster semi-final, but it didn't last long.
The majority of their games have followed a particular order, reflecting their patient approach and the knowledge that physically, and more importantly, mentally, they will never be the first to blink. It underlines the confidence they have in what they do and how they do it.
In four of their six games they have been level at the end of the first quarter. Only against Derry in their Ulster quarter-final have they had any daylight after the first 17 or 18 minutes when they led by 0-4 to 0-1. It is their lowest scoring quarter, with just 1-18 in total, an average of 3.5 points per game. This is their time to size-up opponents and get a feel for what they have to do.
The second quarter has brought more freedom to their play, but, with the exception of the opening game against Cavan, gaps have not significantly been evident.
They 'beat' Down, Kerry and Cork by just one point in each of their second quarters and trailed Tyrone.
But by then the frustration levels were building up in their opponents and, even as they fell behind to Tyrone, there was a sense that they had them where they wanted them. The suffocation process had begun.
Just as the third day of a golf tournament is considered 'moving day,' the third quarter this year has been the defining period in all their victories.
They have outscored all opponents in this period almost threefold, 2-28 to 0-13, a decisive spike on the graph as they move in for the kill.
Think about Penrose kicking the ball away or Paul Galvin being charged down as he attempted a point just 25 metres out. Think about Graham Canty aimlessly slicing a shot off his left foot not long after half-time because there was no other option. This is Donegal at their most intense, moving in to apply that kill.
In all six games they haven't lost a third quarter. Only Kerry have come close in this period to keeping pace with them and, even then, they were cut adrift early in the fourth quarter.
Worryingly for Donegal, the three goals they have conceded in 2012 have all come in the last quarter of games when they have sat on healthy leads.
Niall McDermott's penalty helped Cavan 'win' the last quarter by 1-4 to 0-4, while Kieran Donaghy and Colm O'Neill merely served to bring respectability to the scoreboard for two giants of the game, offering them brief respite from the constriction.
But the last quarter has exposed Donegal's only real vulnerability and is the only one of the four periods that they have not collectively 'won.' Only the Ulster final against Down saw them pull away comfortably and maximise their third quarter dominance.
It's not an area that Jim McGuinness is over concerned about, however, though he accepts there are lessons to be learned. "I would prefer if they were not happening, but I probably felt that we deserved that goal to happen to us against Cork. I don't believe that you can play out three minutes at the end of a game by retaining possession at that level," he said.
"I believe that at some stage someone is going to get their dander up, they are going to put in a tackle and at some stage that tackle is going to result in a turnover, because the referee is not going to have any sympathy on a team that is showboating and retaining possession for the sake of retaining possession."
It is inevitable then that Donegal will strike hardest between the 45th and 60th minutes, when all previous prey have succumbed.
Survive that and Mayo may break the trend of the season.