Sheffield Wednesday have sacked manager Gary Megson, despite the Owls winning Sunday's Steel City derby.
The 1-0 win over Sheffield United moved them up to third in League One.
Chairman Milan Mandaric said he took the decision to give the club the "best chance of achieving our key aim of promotion".
"This was a very difficult decision but one that has been taken with the best interests of Sheffield Wednesday at heart," he added.
Megson's position at Hillsborough has been the subject of much speculation in recent weeks.
Only nine days ago the Wednesday chairman was forced to refute rumours the former Bolton Wanderers boss had left the club.
Yet, after beating their local rivals on Sunday, Megson now finds himself out of work, after just over a year in charge at the club.
"We have 13 games to go of what is a critical season for our club, and this decision has been taken because I believe we have a better chance of achieving our key aim of promotion by making the change," Mandaric added.
"I fully understand this may not be the most popular decision amongst our supporters but I ask them to trust me, as they have done so whole-heartedly during the time I have been at the club.
"Whilst we won what was a huge game last Sunday, I have looked at results before that to reach the conclusion which I believe is the right one for now and the future of Sheffield Wednesday."
Megson took over at Hillsborough in February 2011, replacing Alan Irvine, with the club lying 12th in League One.
At the time, Mandaric described him as a "top-drawer manager".
This season they have won 18 of their 33 matches and lost nine, including three successive league defeats before the win over the Blades.
Former Wolves and Cardiff boss Dave Jones is already being linked with the job.
Mandaric added: "One chapter is closed and another one begins. We must now look forward and I hope to appoint a new manager as soon as possible to help achieve success for this club."
Wednesday are next in action on Saturday when they travel to Spotland to take on Rochdale.