Johnson was speaking ahead of today's clash with West Ham United.
Asked if the squad are behind Postecoglou, he said: "For sure, that's never been in question.
"Games like Thursday hopefully show that all the lads listen to everything that he says and at the end of the day, especially in the Europa League, the game plans have come off perfectly as you also saw in Frankfurt.
"Hopefully we can do that again next week and get to the final."
Indeed, after facing West Ham, Spurs go to Norway for Thursday's Europa League semifinal second-leg at Bodo/Glimt. Tottenham carry a 3-1 aggregate lead.
Johnson added, "It could be massive, it's a big game so for us, it's the most important game. Momentum is such a big thing in football, we're looking to get as much momentum going as we can before next week."