Marti Cifuentes’ return to Loftus Road turned into a nightmare as Queens Park Rangers tore apart his Leicester City side with a dominant display that lifted the hosts above the Foxes in the Championship table.
QPR struck almost immediately, with Koki Saito heading home from close range after latching onto a deflected delivery inside the opening two minutes.
Leicester never recovered from the early blow and were punished again just before the half-hour mark when Richard Kone capitalised on hesitant defending to double the lead.
The hosts ran riot soon after.
Karamoko Dembele picked out the bottom corner to make it three, before Amadou Mbengue capped a devastating first half by catching out Jakub Stolarczyk with a hopeful cross that drifted into the net in stoppage time.
The second period was far calmer, though Leicester were handed a lifeline when Sam Field was penalised for handball.
Bobby De Cordova-Reid struck the post from the resulting penalty, but Silko-Amari Thomas reacted quickest to score from the rebound and claim a consolation goal.
The heavy defeat was especially painful for Cifuentes, who left QPR five months ago following a drawn-out exit that saw him spend the end of last season on gardening leave.
The Spaniard later took charge at Leicester after reportedly helping fund part of the compensation fee required to secure his move.
After a difficult start to the campaign, recent results had eased the pressure on the 43-year-old, with seven points from three December matches suggesting progress.
That momentum, however, was emphatically halted on his return to west London.
In contrast, Cifuentes’ successor Julien Stephan continues to enjoy a revival at QPR.
Despite a slow start, the Frenchman now has Rangers seventh in the table - a marked improvement on their position at the same stage last season.
Four first-half goals set QPR on course for their most emphatic win of the campaign.
Saito’s early header set the tone, Kone showed composure to finish inside the box, and Dembele’s strike at the near post left Leicester reeling before Mbengue’s unlikely effort completed the rout.
QPR looked capable of adding to the scoreline after the break, while Leicester offered little resistance until their late penalty, leaving Cifuentes to reflect on a bruising homecoming.
Queens Park Rangers head coach Julien Stephan told BBC Radio London:
"It was an outstanding first half. The way they played, how they came onto the pitch, how they moved together – with and without the ball – it's never perfect, but it was very close to perfection.
"To score four goals like this, and to create the atmosphere like this with the fans was probably the best first half and best feeling since I started this job.
"When you live something like this, you have to enjoy it, but you also need to be ready to compete immediately and that is what I said at half-time because the game is not just 45 minutes.
"I think we came out very quick and very good in the first 10 or 15 minutes of the second half, and they didn't have many situations, and we could have scored another one. It's a fantastic win."
Leicester City boss Marti Cifuentes told BBC Radio Leicester:
"I'm really angry and really disappointed about the first half. We played below the standards and got punished.
"Credit to QPR, they did really well and it was exactly the kind of game that we knew they like – they were aggressive, they were strong and eager.
"The way we conceded three goals was very poor, and while the fourth one is a fantastic strike we didn't play well in the first half.
"I'm sad for them (supporters) because we want to do well for them and it's hard for us to now get back to Leicester knowing that there were a lot of people who came here to support us, and that's not what we want for them.
"All I can do is try work harder, put in more hours to make sure that the team improves going into the next one, so hopefully on Boxing Day we can have a strong reaction."
