Rangers won its 10th consecutive Scottish Premier League match with Jean-Claude Darcheville and Nacho Novo both scoring twice in a 4-0 win over Hearts on Wednesday.
Rangers continued to lead the league with 65 points, followed by Celtic with 61. Celtic beat Inverness Caledonian Thistle 2-1.
Darcheville scored in the 25th and 44th minutes before coming off at the end of the first half with a hamstring strain. His replacement, Novo, added goals in the 53rd and 69th for a measure of revenge for Rangers' 4-2 loss to Hearts in September.
"We're delighted," Rangers manager Walter Smith said. "We were excellent in the first hour, we nullified Hearts and the strengths that they have and managed to play some good football ourselves."
Scott McDonald scored his 25th goal of the season in the 45th minute and Giorgios Samaras added the other in the 61st for Celtic's win. Marius Niculae scored for Inverness in the 70th.
In other results on Wednesday it was: Aberdeen 1, Motherwell 1; Dundee United 1, St. Mirren 1; Falkirk 0, Hibernian 2; and Gretna 4, Kilmarnock 2.
Motherwell is third in the standings with 45 points, followed by Dundee United with 42.