Boss Brendan Rodgers praised young centre-backs Jack Hendry and Kristoffer Ajer after Celtic dug out a goalless draw against Rosenborg to qualify for the Champions League third qualifier.
The Scottish champions took a 3-1 first-leg lead to Norway but were tentative in a first half which saw an added time save from goalkeeper Craig Gordon prevent Marius Lundemo opening the scoring for the home side.
Celtic had to withstand an aerial bombardment late in the game but Norway defender Ajer, 20, and 23-year-old Hendry stood firm to set up a meeting against AEK Athens with the first game in Glasgow next week.
Rodgers said: “We have achieved the objective, which over the two games was to get through. It was a different type of game to last week.
“Rosenborg played very well in the first half, they obviously needed to come out and take the initiative and they played well.
“We couldn’t quite build the game as well as we would have liked but I was very pleased with the way we defended – that resilience and mentality.
“The second half we changed it slightly to gain more control and I thought in the first 20 minutes we were able to take the sting out of the game and play to our tempo more.
“In the last 20 minutes we had to deal with direct balls into the box and I was very pleased with the two young centre-halves, they really stood up to that.
“Jack Hendry really stood up, especially in the second half, won some great headers and was really dominant. Kris Ajer as well, both young.
“Kris will be a top-class player, he has all the attributes. At 20, he is 6ft 5ins, he can pass the ball, and on a evening like this he showed he can defend. Cristian Gamboa came in again and did very well.
“Tonight was a great demonstration that you can’t always play perfect football, especially away in Europe, when you are under pressure and there are questions asked about your resilience and I thought we stood up to that very well.
“It was a clean sheet and that is always good in Europe away from home.
“We won the tie last week with a great attacking performance and defended well and tonight it was more about being solid and keeping a clean sheet.”
Rodgers will now turn his attention to AEK Athens and added: “I haven’t watched them yet.
“They will be a good side but we are a good side and we hope to show that next week.”