The Republic of Ireland are back in business — and Shane Duffy is at the heart of their revival.

The experienced centre-back knows a thing or two about coming back from the brink, having returned from an ill-fated loan spell at Celtic to star for Brighton this season.

And the 29-year-old’s renaissance has coincided with an upturn in Ireland’s form, to help calm the waters after a choppy start to manager Stephen Kenny’s reign.

As the Boys in Green prepare to face Luxembourg tonight, we take a look at how Duffy has been key to his national team’s resurgence.

Starting with a whimper

Kenny’s time as Ireland boss could not have got off to a more disastrous start.

Having taken over from Mick McCarthy in April 2020, the former Dundalk coach went an incredible 11 games without tasting victory — losing seven of those matches, including a penalty shootout defeat to Slovakia in the Euro 2020 qualifying play-offs.

Most embarrassingly, one of those losses came at home to minnows Luxembourg, with FIFA’s then 98th-ranked nation securing a shock 1-0 win in Dublin.

Those struggles were mirrored by Duffy’s own dip in form last season.

Initial excitement about joining boyhood club Celtic soon turned to despair as the defender struggled north of the border and drew the ire of Bhoys’ supporters over his sub-par performances.

Back to business on the South Coast

Duffy was understandably downbeat about his chances of playing regular first-team football again at Brighton.

Speaking in August, he said: "After the year I had, I was in a really low place and thought [the] Premier League is probably over for me.

"But I have got good people around me and it is the club [Brighton], the club are so good for me and it feels like home for me.

"When I came back after my loan I had a big relief off my shoulders and I felt like I had come home again and the comfort started to come back."

That fresh start has seen the Derry native restore his reputation at the Amex Stadium — filling the defensive slot left by Ben White’s departure with aplomb as Graham Potter’s seventh-place side made a strong start to the season.

An imperious presence

The key to Duffy’s revival has been getting back to what he does best — no-nonsense defending and aerial domination.

Only Watford’s Christian Kabasele (4.46) has made more headed clearances per 90 minutes in the Premier League than the 50-cap international this season (3.8), while he is also in the division’s top 15 players for overall clearances completed (4.9) and aerial duels won (4.2) per 90.

Duffy has been an assured presence at the back for the Seagulls and has also brought that composure to a steadily improving Ireland team over the past few months.

Ireland on the up

After initially struggling to implement his possession-based philosophy, things are starting to come together for Kenny’s Boys in Green.

Following the Luxembourg debacle, they have now lost just once in nine matches — and that was only because of Cristiano Ronaldo’s stunning late double in September’s 2-1 defeat to Portugal.

Duffy is a key figure in Ireland’s first-choice back three and adds experience to a youthful squad that currently contains nine players aged 22 or younger.

He also has a knack for scoring goals, which could be vital in a team that has very few prolific international scorers.

After James McClean (11 goals), Duffy is the joint-second highest scorer in the squad for this month’s fixtures, with six career strikes for his country.

Portugal masterclass

Ireland made amends for their previous defeat to Portugal by holding the Selecao to a commendable 0-0 draw on Thursday night.

And Duffy was one of the stars of the show — marshalling the visitors’ star-studded attack and looking assured with the ball at his feet.

Only Tottenham wing-back Matt Doherty (seven) won more aerial duels than the 6ft 4in colossus (four), as the hosts laid down a marker against their more illustrious opponents.

If Kenny’s outfit and Duffy continue on the same upward trajectory, then things are looking bright for Ireland and their revitalised defensive star.