Celtic's dreams of a domestic treble remain on course as they progressed on Wednesday to the Scottish Cup quarter-finals with a 1-0 win over nine-man Rangers, who also had El-Hadji Diouf ordered off after the final whistle, amid shameful scenes at Parkhead.
An uneventful match turned ugly just after the half-hour mark when two yellow cards in eight minutes saw Steven Whittaker sent off sparking trouble on the sidelines with El-Hadji Diouf involved in a confrontation with Celtic manager Neil Lennon.
The Hoops made their numerical advantage count in the 48th minute when Mark Wilson scored at the second attempt as Sasa Papac, who had blocked his initial shot, lay dazed on the line.
Madjid Bougherra received his marching orders three minutes into stoppage time after picking up his second yellow while Diouf was shown a second yellow card for his protestations at the whistle, in a match where 10 players were booked.
More trouble erupted when Lennon and Rangers assistant manager Ally McCoist had to be separated.
"I was delighted with the performance of the lads, both footballing-wise and discipline-wise," Celtic coach Alan Thompson said, as Lennon remained in the dressing room.
"There is a lot of Old Firm games and we seem to be on a decent run against them."
Rangers manager Walter Smith felt the referee had got carried away by the reaction of the crowd for some of the bookings.
"I don't think we deserved the two sendings off but at least we competed better," said Smith.
"We defended well, especially in the first-half, but in the second-half we were disappointed to lose a goal as early as we did."
The game began at its usual frantic pace and it was the home side that applied the early pressure.
Gary Hooper, who grabbed a double in their last meeting, accelerated past Bougherra and David Weir but Richard Foster was there to mop up the danger.
Celtic 'keeper Lukasz Zaluska then gave his defence a scare when he raced out of his box to confront Diouf on the by-line but Rangers failed to take advantage as his cross was cleared.
The game had been without major incident until Whittaker was sent off in the 36th minute.
He collected his first for a foul on Ki Sung-Yeung and after bringing Emilio Izaguirre clattering to the ground referee Calum Murray produced the red.
All hell then broke out when notorious hothead Diouf and Lennon clashed on the sidelines and McCoist had to be held back from joining in, earning all three a talking to from Murray and the Senegalese striker a booking.
Celtic were immediately handed a chance when a slack backpass from Maurice Edu played Giorgios Samaras in but the Greek striker's shot was superbly blocked by the legs of Allan McGregor.
Scott Brown, Daniel Majstorovic and John Fleck also found themselves booked before the break and more troubled flare in the tunnel as Diouf and Celtic assistant Johan Mjallby exchanged pleasantries.
The Hoops quickly took advantage of their extra man in the second-half as they took just two minutes to take the lead.
A ferocious drive from Wilson cannoned off the head of Papac on the line and with the Bosnian international lying dazed on the ground the Celtic defender followed up with a shot that bounced on the turf and high into the net.
Papac was replaced by Gregg Wylde as Rangers' task got even tougher. Ki sent a 30-yard effort just wide before Samaras held off Kyle Bartley to fire a low shot crashing off the base of the post.
The Greek squandered another chance soon after when he headed Izaguirre's cross straight into the arms of McGregor as Celtic couldn't add to their precarious lead.
Bougherra, booked earlier for a late challenge on Hooper, picked up a second yellow for a foul on Kris Commons three minutes into stoppage time.