Hearts beat Rangers 1-0 in Saturday's first game in the Clydesdale Bank Scottish Premier League and Celtic took advantage later with a 1-0 victory against Aberdeen to move five points clear at the top of the table.
The win allowed the Jambos to move to within two points of Rangers and boosted their case for a three-way fight for the championship or to at least split the Old Firm this season.
Celtic went further ahead at the summit thanks to Anthony Stokes' first-half winner at Parkhead.
The Hoops striker ran on to a Gary Hooper pass in the 27th minute to round Dons goalkeeper Jamie Langfield before stroking in to an empty net.
Garry Kenneth scored a 90th-minute equaliser to salvage a 1-1 draw for nine-man Dundee United in their match at Kilmarnock.
The hosts had gone in front four minutes from the break thanks to Conor Sammon, who netted from close range as he drilled a shot into the bottom left corner.
Kilmarnock had Alexei Eremenko sent off nine minutes into the second half, and he was followed down the tunnel within 11 minutes by visiting players Scott Robertson and Jon Daly, who each received two yellow cards in quick succession.
St Johnstone were denied a hat-trick of wins over St Mirren this season as the clash at McDiarmid Park ended in a 0-0 draw.
St Mirren goalkeeper Paul Gallacher tipped Chris Millar's curling effort on to the bar and saved Collin Samuel's strike in the first half as the hosts extended their unbeaten run to four.
Derek McInnes' hosts have now lost once in their last eight games, but St Mirren created little, with only one effort on target, as they missed the opportunity to build on their 6-1 Scottish Cup success at Peterhead.
Merouane Zemmama missed a penalty as Hibernian became further embroiled in relegation trouble after they lost 2-0 at Motherwell.
Jamie Murphy and Steven Saunders both headed home inswinging Stevie Hammell deliveries midway through the first half to earn Stuart McCall his first SPL win as Motherwell manager.
Zemmama blazed over from the spot a minute before the second half and Hibs failed to seriously test Darren Randolph despite enjoying the territorial advantage in the second period.
Hamilton remain at the foot of the table but they are now three points behind Hibs after securing a 1-1 draw at Inverness.
Mickael Antoine-Curier's penalty on the stroke of half-time cancelled out Dani Sanchez's close-range opener for the hosts at Tulloch Caledonian Stadium.
Visiting substitute Marco Paixao hit the post in the second half and Inverness substitute Russell Duncan had his low shot cleared off the line as neither side managed to find a winner.
