Postecoglou saw his side ease past Raith Rovers at Celtic Park on Thursday night, with a 3-0 win recorded courtesy of goals from Jota, Liel Abada and David Turnbull.
Celtic’s reward is a clash with holders St Johnstone and Postecoglou feels a tough test awaits, though stressed the main thing is the Bhoys are through.
“The important thing is we’re there. It should be a great occasion. It’s something this club wants to continue in”, he told BBC Sportsound.
“It’s a tough opponent, but as I said the most important thing is we’re there. St Johnstone had a tremendous run last year.
“They did well in Europe as well. Irrespective who you play it’s going to be a tough game.”
Celtic fans were hoping to see new signing Georgios Giakoumakis in action after he was named on the bench, but Postecoglou confirmed he picked up an injury niggle while warming up.
Postecoglou revealed that Giakoumakis “did his calf in the warm-up.”
Now Celtic will play the waiting game to see how long Giakoumakis will be out for.
“We’ve sent him for a scan to see how bad it is”, the Celtic manager added.