Celtic came from behind at the break to leave France with a point, but will be aggrieved that it wasn’t three.
Spanish referee José María Sánchez Martínez inexplicably failed to see a stamp on Christie’s instep at the start of the second half.
Having booked Edouard in the first half for diving, he had to either give a penalty or book Christie if he didn’t think it was a foul.
It evidently should have been the former, but Martinez, with a clear view of what was a stonewaller, bottled it as did his linesman.
Celtic had gone in at the break a goal down after M’Baye Niang scored from the spot when Kristoffer Ajer, in a moment of madness, brought him down.
That aside, Lennon would have been happy with his side who had come closest to scoring when Elyounoussi agonisingly failed to get on the end of a ball across the goal to let Rennes off the hook.
Celtic got their due reward in the 59th minute when Christie pounced on a loose ball to play in Forrest, whose quick feet won a penalty.
Christie blasted home to give Celtic a deserved equaliser. Celtic were playing some fantastic stuff and looked the more likely to go on and win the game.
Rennes, who had spent big in the summer, were reduced to amateur dramatics which the referee bought most of the night.
Worse than the penalty he failed to spot, however, was his decision to send off Bayo.
The big striker had replaced Edouard as a late sub. His first main contribution was to go up for a header with Da Silva, which left the defender in a heap.
Tempers, which had been beginning to fray on the French side, boiled over when the Ivorian attempted to latch on to a loose ball in the box after Mendy had spilt Ntcham’s effort.
Mendy got the Equity card out as he rolled around. With Martinez having initially told him to get on with it, he inexplicably changed his mind, no doubt due to pressure from the French side to produce a second yellow.
Another fine move from Celtic led to a good chance for Christie, but he couldn’t dig the ball out of his feet and the resulting corner came to nothing.
Neil Lennon will be happy his team’s performance and, with Lazio losing to Cluj, will be looking forward to a revenge mission against the Romanians at Celtic Park in two weeks time to lay down a serious marker in the group.