Modern-day centre-half O'Shea is at the heart of O'Neill's realm for good reason
How do you like your centre-backs? There was a time when they came out grizzled and mean, and bristling with the menacing aura of bloodthirsty cannibals who liked to feast on the raw meat that was centre-forwards.
Norman 'bites yer legs' Hunter at Leeds, Bill Foulkes of the Manchester United league and European Cup winners of the mid-'60s, and the aptly named Ron 'Chopper' Harris at Chelsea, were typical of the breed which flourished as soccer entered the television age.
Later generations largely followed the template set by their forebears.
These guys would - and were expected to - throw their head into situations where they risked getting them kicked off.
They often emerged bloody, but unbowed, and took pride in keeping 'their' man scoreless, usually a big striker.
Mick McCarthy, former Man City and Republic centre-back, and of course, a former Irish manager, was typical of the old-style defender.
McCarthy and Kevin Moran enjoyed a fruitful partnership at the heart of the rearguard in Jack Charlton's team.
I recall a funny incident in October 1987 when the Republic played Bulgaria in their last match of the European Championships qualifying campaign.
For the second half, I left the press box and stood behind the home dugout to get a different perspective at ground level. You'd get away with that waving a press pass in those days.
In the away leg, Big Mick had felt aggrieved when he was fouled in an incident that led to a Bulgarian goal. He promised revenge on the offender when they came to Dublin.
As it transpired, yer man got called on by the Bulgarian boss in the second half.
He trotted confidently on to the pitch towards the centre-forward position, but McCarthy had him in his sights.
He glared, and snarled to Moran - "Kevin, Kevin, leave that f****r to me" and pointed menacingly at the Bulgarian, who promptly altered course and headed back to the safety of midfield. No 'mano a mano' for him with McCarthy.
It's a lot different now since the advent of the Premier League changed English soccer irrevocably.
The huge sums of money available, the massive influence of continental football, and advances in technology and sports science, have combined to produce a sleeker, more athletic, more cerebral brand of central defenders.
Even if they wanted to, the lads at the heart of a defence cannot indulge themselves solely in one-to-one aerial and ground challenges because of the fluid movement between strikers and midfielders.
Dare I say, they have to be more intelligent, quicker on their feet, and more aware of moves developing at high tempo between the centre-circle and the 'D' on the edge of their own penalty area.
If they slip up, or are lured slightly out of position, particularly at international level, the consequences can be fatal in competitive matches, as the Irish back line found when they were caught out by the Slovakian break which led to a 14th-minute goal by Miroslav Stoch.
There it was in a nutshell - it's too easy to find yourself chasing shadows at top level, so muscle, brawn, and snarling intimidation per se, has had its day.
That said, John O'Shea, skipper against Slovakia, who played in his 110th international at the Aviva Stadium last night, retains special category status in this Irish team.
O'Shea is a big man, able to put himself about, but he would never be known as 'chopper' or 'killer' to his mates - or to opposition strikers.
He is now the leader of the defence, the organiser and director, and O'Neill would surely love to wrap him in cotton wool between now and the start of Euro '16.
The manager, aware that O'Shea is needed by his club on Saturday against West Brom, took him off early in the second half of a competitive 'friendly'. O'Shea has nothing to prove to the manager.
Of the 12 qualifying games, including the two playoff matches with Bosnia & Herzegovina, O'Shea started 10 of them.
He was partnered five times by Marc Wilson, three by Richard Keogh and by Ciaran Clark twice.
O'Shea has scored only three times in his international career, but the one in Gelsenkirchen for a hugely valuable 94th-minute equaliser in October 2014, proved significant for qualification.
Provided he stays fit throughout the rest of Sunderland's battle against relegation, the Waterford native is a certain starter against Sweden on June 13.
If all of O'Neill's players report hale and hearty for duty, then O'Shea's most likely centre-back partner will be Wilson.
O'Neill likes the tried and trusted, if at all possible, and he tends not to change any of his starting back four unless his hand is forced by injury.
If it's not Wilson, then the candidates to play alongside O'Shea are, as of now in descending order, Richard Keogh, Ciaran Clark, Alex Pearce, Shane Duffy, and Paul McShane, although Duffy's display against Switzerland suggests he could be a surprise contender.
Keogh has that willingness and tenacity that is reminiscent of the traditional centre-back.
Clark, of relatively slim build and comfortable with the ball at his feet, could also be handed the responsibility without fear.
One aspect that is a loss from the days of yore is a genuine threat from our centre-backs at corners.
On that big day in 1987 against Bulgaria, the Irish goals came from the centre-halves; Moran and Paul McGrath raiding forward.
O'Shea's goal against Germany was the only, albeit very welcome, score by an Irish centre-back in the qualifying series.