The SPL champions inflict a first home defeat of the season on the Dons as goals from Lassad and Mulgrew see the visitors return to winning ways
The defeat was the Dons first at Pittodrie and only their second since they met the Scottish Premier League champions at Celtic Park on the opening day of the season.
Craig Brown made only the one change to the side that thumped St Mirren last weekend, with Clark Robertson dropping out to be replaced by experienced midfielder Gavin Rae.
In the opposite dug-out, Neil Lennon rang the changes once again as he looked to avoid going four league games without a win, as the Hoops boss brought in Mikael Lustig, Beram Kayal and Tony Watt to replace the injured pair of Scott Brown and Joe Ledley as well as striker Miku.
The home side started the brightest, as both Niall McGinn and Jonny Hayes put the Celtic defence under pressure early on, but neither of them could find the way towards the goal guarded by Fraser Forster.
After the initial burst from Aberdeen, Lennon’s side gained more of a foothold in the fixture, with Victor Wanyama having a chance from a corner and then Georgios Samaras finding his shot deflected for a corner after a cut-back from Watt.
Celtic continued to pile on the pressure, with Kris Commons crossing from the right wing after Aberdeen had failed to properly clear a corner and that allowed the Scotland international to find Watt inside the box, but his chance went wide.
As the game reached the half-time break the visitors should have taken the lead as Lustig got into a corner from the left by Mulgrew, but the Swede’s header was poor and sailed wide.
The second half started with the SPL champions once again on the front foot, especially from corner kicks, as they looked to find Wanyama with the delivery from Mulgrew, but the Kenyan midfielder could not direct his effort on target.
Lennon’s side continued to turn the screw on the Dons defence, with Mulgrew trying his luck with a free kick from 25 yards out, but Langfield got behind the ball to save comfortably.
Celtic got the opener with just over quarter of an hour remaining as Wanyama marched forward with the ball before unleashing a strike from the edge of the area which smacked off Langfield’s left hand post and into the path of Lassad, who had the simplest of tasks to claim his first goal for the Hoops.
A couple of minutes later one became two, as Samaras cut inside from the left-hand side and crossed for Mulgrew, who from the middle of the Aberdeen penalty area directed his effort beyond Langfield to double the advantage.
The SPL champions should have extended their lead late on as Efe Ambrose got onto the end of a Mulgrew free kick, but his header was ruled offside as Lagfield’s save went into the path of Wanyama, who headed home, as Celtic were forced to settle for the two-goal victory.