A late strike by substitute Nigel Hasselbaink gave St Johnstone an unlikely share of the spoils against Celtic in a 1-1 Clydesdale Bank Premier League clash at McDiarmid Park.
In the 37th minute of a first-half controlled by the champions, defender Efe Ambrose scored his second goal in two games after costing the Hoops twice in their 3-0 Champions League last-16 defeat against Juventus a week ago.
The Perth side, who had deprived Celtic of five points in their previous two meetings this season, made a better fist of the second-half and had the ball in the net twice, only to see both efforts ruled out for offside but with eight minutes remaining Hasselbaink, on for Rowan Vine, curled a fantastic shot past Fraser Forster to stun the Parkhead side.
The visitors were in complete control and in the sixth minute Lassad headed an Emilio Izaguirre cross past the far post from around eight yards.
Steve Lomas's side were offering little in reply although in the 15th minute Charlie Mulgrew's intervention at the edge of the box stopped Steven MacLean getting through to face Forster but the corner came to nothing.
In the 34th minute Alan Mannus saved the home side when a one-two between Gary Hooper and Joe Ledley saw the Welshman cut the ball back for Lassad Nouioui but his first-time effort from eight yards was blocked by the keeper. Three minutes later, though, Celtic were ahead.
With the Saints defence sleeping, Kris Commons worked a quick corner to Izaguirre and when he whipped in his cross Ambrose rose to flick a header past Mannus, who this time was helpless.
The Nigeria defender performed his now trademark somersault celebration behind the goal before racing all the way over to the technical area to hug Neil Lennon, acknowledging his gaffer's backing in the wake of the Juventus defeat.
In the 65th minute, with the Perth men coming back into the game, Hasselbaink came on for Vine while James Forrest replaced Commons for Celtic, by now, a little disjointed.
In the 82nd minute, however, the Perth side got just rewards for their second-half efforts when Hasselbaink picked up an Mehdi Abeid pass, turned and curled shot from the edge of the box past Forster and into the far corner of the net.