Both teams came into the game without conceding a goal in their last outing, but Niang handed Rennes a first-half lead.
The Senegalese converted a 38th-minute penalty after sending Fraser Forster the wrong way after some rash defending from Kristoffer Ajer.
It was the visitors’ turn to get their own penalty when referee Maria Martinez pointed to the spot after James Forrest tumbled under Damien Da Silva’s challenge in the 59th minute.
Ryan Christie kept his cool to blast past Senegal’s Edouard Mendy.
Vakoun Bayo replaced Odsonne Edouard in the 84th minute and was booked for an aerial challenge which resulted in Da Silva being stretchered off in the 89th minute.
He was sent off a minute later for clipping goalkeeper Mendy. Despite Rennes’ numerical advantage, the game ended with no winner.Lazio, while Celtic host CFR Cluj.