Georgios Samaras's second-half double in the Old Firm derby at Ibrox earned Celtic a 2-0 win and took them four points clear of Rangers at the top of the Clydesdale Bank Premier League.
The Hoops striker pounced on a Joe Ledley punt over the top in the 61st minute before rounding Allan McGregor and sliding into an empty net.
The Greece international then steered a spot-kick past the Light Blues goalkeeper after he had been felled in the box by Rangers defender Madjid Bougherra to increase Celtic's advantage at the top of the table.
Rangers midfielder Lee McCulloch had a header cleared on to the bar by Celtic defender Emilio Izaguirre in the fifth minute.
The minute's silence before kick-off to commemorate the 40th anniversary of the Ibrox disaster, when 66 people died in a crush leaving stairway 13 after a drawn Old Firm game, was perfectly observed.