The Scottish champions went into tonight's second leg in Iceland defending a 2-0 lead, but they were quickly given a scare by the Champions League debutants.

Stjarnan attacker Olafur Finsen stunned Ronny Deila's side by breaking the deadlock after less than 10 minutes, cutting inside his marker before clipping the ball past Craig Gordon in the Celtic goal.

Despite falling behind, it was the visitors who looked in control, although their best chance of the opening 20 minutes saw Nadir Ciftci fire off target from an acute angle.

Celtic did have the ball in the back of the net midway through the first half when Dedryck Boyata swept home a deflected free kick, but the summer arrival, who opened his account for the club in last week's first leg, was denied by the offside flag.

The equaliser did arrive shortly after the half-hour mark, however, as Nir Bitton glanced home a Stefan Johansen delivery following some questionable goalkeeping from Gunnar Nielsen.

Stuart Armstrong was the next to threaten for the Bhoys, but Stjarnan fired another warning shot shortly before half time when Daniel Laxdal drilled an effort narrowly wide of the target.

The tie was effectively put to bed with Celtic's second away goal of the night just four minutes after the interval, however, as Scott Brown squared the ball to Charlie Mulgrew, who proceeded to pick out the bottom corner with aplomb.

Leigh Griffiths, who missed a penalty in the first leg, almost made amends within minutes of coming on as a sub when he poked the ball goalwards with his first touch, but it dribbled narrowly wide of the upright.

Griffiths turned provider with a little over 10 minutes to go, but Ciftci could only drag his shot wide having been played through on goal by his new strike partner.

Celtic kept pushing for a third on the night, and they finally found it in the final minute of the match when the lively Griffiths exchanged passes with Gary Mackay-Steven before slotting home.

There was even time for a fourth to make it 6-1 on aggregate as Johansen put the icing on the cake with virtually the last kick of the match.

Celtic will now face FK Qarabag of Azerbaijan in the next round.