Neil Lennon was left fuming after Almen Abdi's late penalty salvaged a point for an understrength Udinese in their enthralling Europa League Group I clash with Celtic at Parkhead.
The Hoops got off to a perfect start when midfielder Ki Sung-yueng scored from the spot in the third minute after striker Gary Hooper had been fouled by Joel Ekstrand.
The game ebbed and flowed, especially in the second half, and it looked like Lennon's men would see the game out.
However, in the 86th minute Hooper, back defending, gave away a penalty when he clipped Neuton in the box and Abdi sent Lukasz Zaluska the wrong way from the spot.
"It's a shocking decision," Lennon said afterwards. "It cost us three points which we deserved against a very good side. We kept our discipline well and their goalkeeper made some wonderful saves. The referee was looking right at it and it's really hard to take. He (Hooper) has done everything he can to get out of the way."
It was hard luck for Celtic who have one point from two games following their 2-0 defeat by Atletico Madrid in Spain earlier in the month.
However, it was the Hoops who took the early lead after Hooper was clumsily pulled down by Ekstrand. Yildirim did not point to the spot at first but after appearing to wait for some guidance from his linesman, he confirmed what had looked obvious.
Ki slammed the penalty high past Handanovic, but the Bhoys couldn't hold out and were denied three points by Abdi's late sucker-punch.
Elsewhere, Damien Duff returned to action as Fulham won 2-0 at Odense thanks to a brace from Andy Johnson.
Stoke came from behind to beat Besiktas thanks to Jon Walters' penalty and a goal from Peter Crouch. Goals from Chris Burke and Wade Elliott also saw Birmingham recover from falling behind to beat Maribor in Slovenia.