Northern Ireland had chances to extend their lead in Belfast, but O'Neill admitted the tempo dropped as legs began to tire. It comes with the nature of youth.

Much has been made of O'Neill's Northern Ireland 2.0, which has saw a reliable and experienced group of players gradually replaced by an exciting bunch of youngsters, who are raw but highlighting their potential on the international stage.

Liverpool defender Conor Bradley, 21, has often been the focal point of the excitement in the fan base, but Trai Hume, who captained Northern Ireland on Thursday at the age of 22, Shea Charles and Isaac Price, both 20, are also into double figures for caps and show that the future is bright.

"A lot of international careers ended in the last 12 months," he added.

"You are never going to have a ready made team to put in place, it has to go through some pain."

The pain O'Neill is referencing came when he stepped back into the role following the departure of Ian Baraclough.

With several first-team players out injured, O'Neill had to fast track youth into his squad and there were the inevitable growing pains as his team found their feet and missed out on Euro 2024 qualification.

However, the campaign ended with positive shoots with a win over Denmark and victories over Scotland, Andorra and now Luxembourg have followed.

There has also been a draw with Romania and a defeat by Euro 2024 winners Spain in that time.

"Within those six games we have played teams who we would expect to beat and also played teams we have got good results against as well," said O'Neill, who added the "mood has always been good" in the camps since his return.

"We have [momentum]. Confidence is growing and a lot of these lads came into international football and didn't win a lot of games at the outset.

"Now they are starting to know how it feels to win. You can see in the dressing room what it means to them.

"A lot of them are going to have long international careers. There are always periods with Northern Ireland where you don't win, and play through some difficult times. The best players have always had to do that.

"There is a lot of growth to come in the team, there's no doubt about that.

"We have to keep letting them develop naturally themselves and not put too much pressure on them. Hopefully they will take that into games and give good performances."

Now, the challenge for Northern Ireland is to continue their momentum away to Bulgaria on Sunday.

The Bulgarians were held to a goalless draw by Belarus in their opening match, which means if Northern Ireland can get three points in Plovdiv it puts them in a strong position in Group C3.

Winning the group would open the door to a potential play-off place for the 2026 World Cup and O'Neill says his side are ready to "fully embrace" the campaign.

"It's important. The other game was a draw so if we go to Bulgaria and get a result then we will be in a nice position.

"There's a lot to play for. It's a competition that we have had difficult results in.

"The timing of the competition has been difficult for us and come at transitional periods for our squad.

"We fully understand that if we do well in it then it has particular advantages down the line for us, in terms of opening up possible qualification routes.

"We're taking it as seriously as any of the other competitions."