Last year, Tom O'Sullivan didn't play a single minute of the Munster Championship. He was then parachuted into Kerry's defence for their crucial Monaghan tie as their season hung by a thread. He finished with 0-2 and Kerry lived to fight another day.
The Dingle man put in another superb showing against Kildare two weeks later before he returned to his club where his form carried over during a march to the county final. At the end of 2018, he was named Terrace Talk player of the club championship.
Kerry's long-established problem lies in their defence but the 22-year-old has been key to the improvement in that. This year he has marked Peter Harte, Cillian O’Sullivan, Jamie Brennan, James Carr and Paul Kerrigan. Every single one of them was kept scoreless.
"If you talk to locals in Kerry they say he was quiet. He genuinely does not get the recognition he deserves," Dingle coach Paul Fitzmaurice tells Balls.ie. He was worked with O'Sullivan since he was a boy and seen his development up close.
They say he had a quiet game because he didn’t score. But sure he got his tackles and did his job beyond that. That is the greed of Kerry football. If you don’t score, you are not playing well.
It is the off the ball stuff Tom does. He has a level of intelligence beyond it. He is capable of going forward but for the greater good and Kerry’s defensive structure he has to wipe out Peter Harte and he is a fella willing to do that.
"Even if you go back and watch the National League. He was a nightmare for Shane Walsh. He just stood in front of him, look at it now. Left-hand side of the screen, all day he was just facing Walsh. He is not facing the play, he is focused on the danger man. Hands-on, pressure, needling him and sure Walsh had no influence in Tuam. He kicked a single score."
After ten minutes of the All-Ireland semi-final, O'Sullivan had five possessions and two kick-passes. Harte had none. The All-Star contender entirely neutralised Tyrone's talisman with a textbook defensive display.
Going into the weekend's clash, Kerry would have identified Tyrone's big three as needing particular attention; Cathal McShane, Mattie Donnelly and Peter Harte.
Tyrone strength and conditioning coach Peter Donnelly has done an outstanding job in creating an extremely physical and well-conditioned team. Kerry could not and would not compete on those terms.
Instead, the relied on a player with brains rather than brawn to compete with Harte. At 70 kg, 5'10'' O'Sullivan is the lightest player to play for Kerry on Sunday. For comparison sake, Brian Ó Beaglaoich is closest at 73kg. At the other end of the scale, 6' 4'' Tommy Walsh is an impressive 97kg.
Backroom coaches Donie Buckley and Tommy Griffin will no doubt have dedicated much time to Kerry's defensive structure. Key to it all is knowing when to stick on your man and when to drift. That balance has drastically improved since the Munster final.
Tom O'Sullivan embodies it.
Early in the game, a long ball comes in. O'Sullivan stalks Harte all the way.
He only has eyes for his man, trusting his defence to deal outside of him.
Kerry cancel out every option. The nearest inside man is Harte but O'Sullivan is stuck to him.
With nothing on, Tyrone try to force a pass and the attack breaks down.
Shortly after, Richie Donnelly attacks down the wing into space. However, Harte is more dangerous so O'Sullivan takes the smart option and turns his back on play to track him.
Donnelly has no option so drives into open space and ends up kicking a shot well wide.
Yet O'Sullivan is shrewd and knows when to scramble as well. Mickey Harte played with five forwards, allowing Paul Murphy to be a free defender for Kerry. His job was to hold the centre and ensure Tyrone did not attack the heart of the defence. If he dropped too deep, that would have left space in the middle for strike runners, of which Tyrone have plenty.
"Tom reads a situation quicker than anyone," Dingle's Fitzmaurice explains.
As an under 12, he was quite willing to leave his man because he would read where the ball would go. He could read everything and cut it out. People would be onto him, 'stay on your man!’ But no, he knew right.
In this passage, a ball is delivered long for Harte while Murphy drifts across.
O'Sullivan gets there first but a clear push in the back knocks him and Harte gains possession.
Murphy drifts to Harte while Donnelly goes on the loop. Immediately, O'Sullivan recognises this and shifts across to Donnelly.
The ball is kicked towards McShane and breaks. O'Sullivan stays goal side of Donnelly, Harte stays wide.
Then Kerry scramble. O'Sullivan bites in on the ball forcing it wide, knowing his defenders will drift across to the less dangerous position.
Tyrone move wide because Harte is free. Enright gets there and blocks him down.
That is not to mention his contribution in attack too. His sum total so far this Championship is 1-3 and for Fitzmaurice, that is no surprise. Across an underage career that included an All-Ireland minor medal in 2014 as well as two Hogan Cup wins, he has always been effective on both sides of the ball.
Tom has played everywhere. I had him since he was 12. Now he is a Rolls Royce defender but there were several days we played him in the forwards if it was a game that suits us. If the opposition were bigger we'd put him up there and he'd do a job on them.
In one of the Hogan cup finals, he started at corner-back and went into the full-forward line for the second half.
That is his ability, there this is his attitude. Tom O'Sullivan is now the stand-out favourite for an All-Star in the backs and it has come through meticulous preparation.
"Stretch bands and foam rollers all came in and people were on it, he was doing it way before that. Just so tuned in. He trained away by himself as well even though he was involved in so many teams.
"People go on about burn-out, that young fella played on as many teams as anyone and bar the odd turn of the ankle he never got injured because he minded himself. He did cross country to keep his aerobic fitness up. Worked himself and physically he has come on in his own way. Just pure power in the legs."
Next up is an All-Ireland final against Dublin. While Tadhg Morley and Jason Foley are obvious man-marking options, the unique prospect that is footballer of the year contender Con O'Callaghan will demand a particular skill-set both in terms of speed and steel.
Peter Keane could do worse than look to his outstanding corner-back for the job.