Neil Lennon's men were forced to come from behind in order to carve out an advantage in their Champions League qualifier ahead of the return leg in Finland next week
Victory for the Hoops comes just days before they open up their SPL campaign against Aberdeen, but they will have to worry about the trip to Helsinki next week after Rasmus Schuller scored an away goal.
Neil Lennon’s side started quickly and almost claimed a goal within 17 seconds. Adam Matthews played the ball long for Georgios Samaras, who flicked it onto Hooper, but the English striker couldn’t find the finish to give Celtic an early lead.
The home side continued to pile on the pressure, with Hooper racing in from the right hand side and crossing into the box, but before he could find a player in green and white, Timi Lahti managed to clear the ball for a corner.
There were then claims from the home support for a penalty, as James Forrest tried to get his head onto a cross from the left by Samaras, but put the ball wide as the Celtic winger felt he was pushed by the defender behind him.
Forrest then turned provider, as he crossed from the right wing attempting to find Hooper, before Joe Ledley appeared late to unleash a powerful shot that just went wide.
Ledley then had a superb opportunity to put the Scottish champions into the lead as he latched onto a Victor Wanyama knockdown from a Matthew cross, but his strike was palmed away for a corner by HJK keeper Ville Wallen.
The Finnish side began to claw their way back into the game when Demba Savage got the ball into the box after a cross from the right wing by former Hamilton Accies defender Sebastian Sorsa, but Matthews slid in to clear the ball away from danger.
HJK continued to press, with Joel Perovuo having an attempt from just outside the area that had Fraser Forster scrambling to his right in order to tip the ball away for a corner ahead of half-time.
The second half started miserably for the Hoops as Schuller raced down the right wing into the box and, after Forster had saved the first effort, the HJK midfielder smacked the ball into the back of the net to give the Finns the away goal.
Celtic almost replied immediately, as Kris Commons received the ball just outside the box and smashed it towards goal, but unfortunately for the Scottish international his strike came back off the post before deflecting off Wallen and away from danger.
Lennon’s side finally got on level terms with ten minutes gone in the half, as Samaras claimed the ball on the left wing and played a cross on the deck for Hooper to stroke the ball home.
And, just five minutes later, Celtic went into the lead as Commons swung in a corner from the right wing for Mulgrew to crash a downward header beyond the helpless Wallen and into the net.
Celtic continued to put the foot to the floor as they looked for a comfortable lead going into the second leg, but Forrest saw his cross cleared before Hooper or Samaras could latch onto the ball.
Unfortunately for Celtic they couldn’t find the third goal that would have gave them a security blanket as they make the trip across the North Sea towards Helsinki next week.