Aberdeen sacked manager Jim Goodwin for what the club described as "an unacceptable run of results" after a 6-0 thrashing at the hands of Hibernian on Saturday.
Goodwin was given an ultimatum by the Dons' board after Aberdeen were dumped out of the Scottish Cup by sixth-tier Darvel on Monday.
But they were further embarrassed at Easter Road by a Hibs side that had also been struggling for results.
Josh Campbell scored a hat-trick, while Elie Youan, Kevin Nisbet and Will Fish were also on target.
Aberdeen have won only once in 10 games since the World Cup break to slip to seventh in the table.
"Following an unacceptable run of results since the World Cup break, the club confirms it has parted company with Jim Goodwin and first team assistant manager Lee Sharp with immediate effect," Aberdeen said in a statement.
At the top of the table, Rangers narrowed the gap on leaders Celtic to six points with a 2-0 win over St. Johnstone.
James Tavernier's penalty and Glen Kamara's strike continued Rangers' unbeaten record under Michael Beale.
But St Johnstone were left aggrieved about the award of the spot-kick that led to the opening goal and two red card calls before the break.
Nicky Clark was shown a straight red for a challenge on Ryan Jack.
Moments later Jack was only shown yellow for a similar foul and referee Willie Collum stood by his initial decision despite being asked to review the incident by VAR.
The bottom four are now all tied on 20 points after Ross County moved off the foot of the table with a 3-0 win over Kilmarnock.
Motherwell remain mired in the relegation fight after losing 1-0 to St. Mirren.