Match ends, Birmingham City 1, Queens Park Rangers 4.
Birmingham City 1-4 Queens Park Rangers
QPR climbed seven points clear of the Championship drop zone as Gianfranco Zola's Birmingham City lost for a ninth time in 14 games since he took charge.
Birmingham-born Matt Smith headed home fellow January signing Luke Freeman's corner to put QPR ahead on 18 minutes.
Conor Washington shot home to double the lead two minutes after the break.
Idrissa Sylla headed a close-range third, then Yeni N'Gbakoto struck a late fourth before Emilio Nsue pulled one back in injury time for Blues.
City's defeat was their heaviest under Zola - and their worst at St Andrew's since the 8-0 club record defeat by Bournemouth in October 2014, the game before Zola's predecessor Gary Rowett took charge.
Blues were without suspended midfielders Craig Gardner and David Davis, injured centre-half Michael Morrison and top scorer Lukas Jutkiewicz. He was out with a hamstring injury suffered in training after scoring six of the nine goals Blues had managed in their previous 13 games under Zola.
And they were further disrupted by the first-half loss of Cheick Keita, but that was after the first goal from Smith, who was denied a second by a fine save from Tomasz Kuszczak.
Washington stunned City with his early second-half strike, blasting home after the hosts failed to clear a cross, before two goals in the final six minutes.
Sylla headed home a right-wing cross from Pawel Wszolek, before N'Gbakoto's long-range shot wrapped up a victory spoiled only by Nsue's injury-time consolation goal.
Although the Hoops, who climb three places to 16th, have won comfortably more points away from home in the Championship this season (21) than they have at Loftus Road (16), the size of this defeat was still a shock.
Blues have now picked up just six points in 12 league games under Zola. Only Bristol City (five points) have won fewer since his appointment on 14 December - and they have played two games fewer.
Smith's road back to St Andrew's
Birmingham-born Matt Smith played for three Midlands non-league sides, Redditch United, Evesham Town and Solihull Moors, while he was a student at Manchester University.
After graduating with a first-class degree in international management with American business studies, he made his Football League debut with Oldham Athletic in 2011, since when he has also played for Leeds United, Fulham and Bristol City.
His father Ian Smith, who also played north of the border for Queens Park and Hearts, made two appearances for Birmingham City in 1975.
What they said
Birmingham City boss Gianfranco Zola:
"The result was very painful. Probably our worst performance. It was very frustrating. The situation is what football is all about.
"They were superior and we couldn't cope with the physicality of the opposition. On the other hand we couldn't produce enough quality to cause them problems.
"In the end we lost badly and I feel sorry for the players as it is hard for them at the present time."
QPR manager Ian Holloway:
"Matt Smith is a player I've always wanted. He is still catching up to speed. He is such a handful and scored with a brilliant header.
"The last thing you want is him towering above you. I am delighted for him as he is a wonderful kid. And what was also pleasing was that all my strikers scored.
"There is now a good feeling within the team. It shows where we are trying to get. The standard is so high and tough. We had some bad results which knocked our confidence but obviously I hope that we can build on this win."
- 25CogleySubstituted forFrei Koyunluat 45'minutes
- 33KeitaSubstituted forRobinsonat 31'minutesBooked at 56mins
- 7TescheBooked at 21minsSubstituted forStorerat 82'minutesBooked at 87mins
- 21Frei Koyunlu
- 6LynchBooked at 50mins
- 41ManningBooked at 90mins
- 3BidwellBooked at 82mins
- 15WszolekSubstituted forLua Luaat 85'minutes
- 17SmithSubstituted forSyllaat 80'minutes
- 9WashingtonBooked at 79minsSubstituted forN'Gbakotoat 85'minutes
- 28Lua Lua
- Andy Davies
- Shots on Target
Second Half ends, Birmingham City 1, Queens Park Rangers 4.
Goal! Birmingham City 1, Queens Park Rangers 4. Nsue (Birmingham City) right footed shot from the right side of the box to the bottom left corner. Assisted by Che Adams.
Attempt missed. Kerim Frei (Birmingham City) right footed shot from a difficult angle and long range on the left is close, but misses the top left corner from a direct free kick.
Ryan Manning (Queens Park Rangers) is shown the yellow card for a bad foul.
Jerome Sinclair (Birmingham City) wins a free kick on the left wing.
Foul by Ryan Manning (Queens Park Rangers).
Goal! Birmingham City 0, Queens Park Rangers 4. Yeni N'Gbakoto (Queens Park Rangers) from a free kick with a right footed shot to the high centre of the goal.
Jack Storer (Birmingham City) is shown the yellow card for a bad foul.
Foul by Jack Storer (Birmingham City).
Ryan Manning (Queens Park Rangers) wins a free kick in the attacking half.
Jerome Sinclair (Birmingham City) wins a free kick on the right wing.
Foul by Kazenga Lua Lua (Queens Park Rangers).
Substitution, Queens Park Rangers. Kazenga Lua Lua replaces Pawel Wszolek.
Substitution, Queens Park Rangers. Yeni N'Gbakoto replaces Conor Washington.
Goal! Birmingham City 0, Queens Park Rangers 3. Idrissa Sylla (Queens Park Rangers) header from very close range to the bottom left corner. Assisted by Pawel Wszolek with a cross.
Jake Bidwell (Queens Park Rangers) is shown the yellow card for hand ball.
Hand ball by Jake Bidwell (Queens Park Rangers).
Substitution, Birmingham City. Jack Storer replaces Robert Tesche.
Attempt blocked. Kerim Frei (Birmingham City) right footed shot from outside the box is blocked. Assisted by Greg Stewart.
Substitution, Queens Park Rangers. Idrissa Sylla replaces Matt Smith.
Hand ball by Conor Washington (Queens Park Rangers).
Attempt missed. Nsue (Birmingham City) left footed shot from the centre of the box is close, but misses to the left. Assisted by Jerome Sinclair with a cross.
Corner, Birmingham City. Conceded by Jake Bidwell.
Foul by Kerim Frei (Birmingham City).
Darnell Furlong (Queens Park Rangers) wins a free kick in the defensive half.
Paul Robinson (Birmingham City) wins a free kick in the defensive half.
Foul by Matt Smith (Queens Park Rangers).
Offside, Birmingham City. Che Adams tries a through ball, but Jerome Sinclair is caught offside.
Greg Stewart (Birmingham City) wins a free kick in the defensive half.
Foul by Pawel Wszolek (Queens Park Rangers).
Attempt blocked. Conor Washington (Queens Park Rangers) right footed shot from the left side of the box is blocked. Assisted by Joel Lynch.
Attempt missed. Jerome Sinclair (Birmingham City) header from the centre of the box is close, but misses to the left. Assisted by Greg Stewart with a cross following a set piece situation.
Nsue (Birmingham City) wins a free kick on the right wing.
Foul by Conor Washington (Queens Park Rangers).
Jonathan Grounds (Birmingham City) wins a free kick in the defensive half.
Foul by Matt Smith (Queens Park Rangers).
Corner, Queens Park Rangers. Conceded by Tomasz Kuszczak.
Attempt saved. Grant Hall (Queens Park Rangers) header from the centre of the box is saved in the top left corner. Assisted by Ryan Manning.
Corner, Queens Park Rangers. Conceded by Jonathan Grounds.