With Rangers having dropped points earlier in the day the pressure was on Celtic to capitalise by seeing off Dundee in the Scottish Premiership encounter.
Dundee took the lead with 26 minutes on the clock, but a quickfire double from Giakoumakis in the 34th and 38th minutes put Celtic in charge.
The visitors though looked like they might nick a point when Ryan Sweeney levelled in the 60th minute, but Giakoumakis rose to the occasion again, scoring with four minutes left to seal all three points for Celtic.
Postecoglou was delighted and insists that is why he splashed the cash on the striker.
“He’s been good”, Postecoglou was quoted as saying by the BBC.
“He’s been working awfully hard without always getting the rewards. He’s been unlucky at times.
“That’s why I brought him to the club.
“You saw with the opposition putting so many players in the box, we needed someone with presence and he’s got bags of it.”
Celtic now boast a three-point lead over Rangers at the top of the Scottish Premiership table, with 27 games played.
