Across his two spells as Northern Ireland boss, Michael O'Neill has been blessed with no shortage of centre-back talent.

Jonny Evans, Aaron Hughes, Gareth McAuley and Craig Cathcart were mainstays of his first stint in charge - so much so that, in some of the biggest games of O'Neill's managerial career at Euro 2016, the quartet all started across a flat back-four.

Since returning to the job four years ago, O'Neill has switched to three at the back, with Sunderland duo Trai Hume and Dan Ballard providing an injection of Premier League quality in what remains a side largely drawn from the Championship and League One.

But with Hume, something of a Swiss army knife in the squad, covering the injured Conor Bradley on the right flank and even starting in centre midfield against Ukraine last month, and Ballard presently nursing an injured hamstring, change has been required through this Nations League campaign.

Despite those forced alterations in defence, the side go into their concluding Group B2 fixtures against Ukraine and Hungary top of their pool and the only side at any level of the competition yet to concede a goal.

At the heart of their defensive efforts have been Ruairi McConville and Tom Atcheson, two young centre-backs already described by their international manager as having "no ceiling".

At 21-years-old, Norwich City's McConville is the more senior of the pair.

Having been given his debut off the bench at home to Belarus two years ago this week, among the former Brighton man's early international assignments was trying to keep a rampant Alexander Isak in check during a 5-1 defeat by Sweden.

In the short time since he has looked an increasingly commanding figure, leading this Nations League group in clearances made with both head and boot.

"It would be unbelievable to keep that record for these last two games and go the whole of the campaign," he said of what is Northern Ireland's longest run without conceding a goal since 2017.

McConville notes that the streak is a team effort and product of collective work-rate, rather than just the defensive three alone.

"We're a team that works hard, a team that doesn't want to give anything up.

"We're confident in ourselves and we know that we're a good side."

It is McConville who has taken on the Ballard role in the middle of the defence for the past three games, with Atcheson on the right and Oxford United's Ciaron Brown, himself superb through the campaign so far, playing from the left.

On the developing understanding between an emerging unit, McConville added: "We're enjoying playing together.

"It's still early days together and we have to keep taking it game by game and doing what the gaffer tells us and the work on the training pitch.

"We don't have much time together when we're here [in international camp] so it's important to do all we can."

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After 16 caps, McConville is a relative veteran compared to Atcheson, who made his international bow in a friendly against Wales in March at a time when he had only four senior club starts to his name at Blackburn Rovers.

The most recent of those had come under O'Neill, then in a short stint as caretaker manager at the Championship club.

Clearly impressed by what he saw from the now 20-year-old at Ewood Park, Atcheson made his first Northern Ireland start against Guinea in June, a game in which he scored the winner with a fabulous flick before later being shown a red card.

Some 428 minutes into his international career, Atcheson is still to experience what it feels like to concede a goal.

The England-born defender feels Ballard "is definitely a big miss" to the side, but believes the squad's understanding of O'Neill's desired system is an asset to those who have starred during the Sunderland man's latest absence.

"I feel like everyone knows what they need to do, everyone knows their job, the details of the formation we play and system," he said.

"That's so key and I think that's why we're so solid defensively.

"It's a team thing, we're set up right, we're very on it all the time and everyone gives their all."