The 31-year-old drove home from the edge of the box at Stamford Bridge to move Harry Redknapp’s side to within five points of safety and prevent Chelsea from reclaiming third place from Tottenham Hotspur.
“They worked their socks off and they got their rewards. We deserved it and it was a fantastic performance,” said QPR manager Redknapp.
“They have set the standard tonight and to get out of this mess, they have to do it every week.”
Newcastle United had announced earlier in the day that they had accepted a bid for striker Demba Ba from Chelsea and last season’s Champions League winners looked like they needed the extra fire-power against their London rivals.
Interim coach Rafael Benitez made five changes to his starting line-up, with Ashley Cole, Ramires, Juan Mata, Eden Hazard and the injured Petr Cech dropping out, and the changes were to prove costly.
German winger Marko Marin made his first league start for Chelsea but his only contribution of note was an ugly fourth-minute challenge on Stephane Mbia for which he was lucky to escape with only a caution.
Marin did tee up Victor Moses to shoot wide from close range early in the second half, while Julio Cesar saved brilliantly from Fernando Torres and Frank Lampard had a goal ruled out for offside, but Chelsea were below-par.
Punishment arrived with 12 minutes to play, when Adel Taarabt teed up Wright-Phillips to find the bottom-left corner from 20 yards and bring Chelsea’s four-game winning run to a juddering halt.
QPR boss Harry Redknapp hailed the win as a turning point in his side’s season.
The win was only QPR’s second league victory of the season and moved Rangers level on points with second-bottom Reading, five points adrift of safety.
But the manager believes the impact of the result will be hugely significant in the context of the relegation battle and strengthen his chances of bringing in new recruits in the January transfer window.
“I had a good meeting with (the players) after the Liverpool game (QPR lost 3-0) and I think I convinced them I thought we could stay up,” he said.
“You probably thought I was mad, but I didn’t go home thinking we are doomed. I thought we could turn it around if we can get this lot working and get someone in the window. And tonight (Wednesday) has proved that.
“Most important, we worked hard. We grafted and if we do that until the end of the season, we will win some games. The other teams down there will be thinking: ‘That’s not very good.’ I’ve been there.
“That will send shocks through everybody and we’ve got to make the most of that tonight.”
Chelsea's interim manager, Rafael Benitez, blamed his side's defeat on fatigue and admitted they cannot afford further slips if they are to close the 14-point gap on leaders Manchester United.
“A lot of things went wrong today,” said Benitez.
“We knew we were playing against the bottom-of-the-table side and we spoke about that. We knew we had to be focused but we did not have the tempo and some players may have been tired.
“It was going wrong against a side who played deep and were organised.”
Benitez admitted striker Fernando Torres is one of the players who needs a rest and says he hopes to have completed the signing of Newcastle United forward Demba Ba before the FA Cup tie at Southampton on Saturday.
The manager made changes to his line-up and said: "We can't carry on with the same players. We were playing the bottom of the league at home and you have to trust your players.
"The main thing is we were a bit tired and couldn't produce the pass, the intensity and the movement.
"We have to have everything almost perfect now. When you lose a game it is more difficult, but I can't be thinking about the number of points -- only the next game.
"We have the FA Cup now, then we have to think how we can get three points from every game."
Meanwhile, Everton bolstered their bid for Champions League football by coming from behind to win 2-1 at Newcastle.
Papiss Cisse did his best to prove there is life after his Senegal team-mate Ba by heading Newcastle into a second-minute lead after goalkeeper Tim Krul’s long kick was allowed to bounce on the edge of the visitors’ box.
Leighton Baines produced a goal-of-the-season contender to equalise, however, rippling the net with a magnificent 30-yard free-kick that left Krul grasping at thin air.
Substitute Victor Anichebe completed the comeback on the hour, tapping in Nikica Jelavic’s low cross barely ninety seconds after coming on to send Everton up to fifth.
Liverpool reinvigorated their push for European football by sweeping Sunderland aside 3-0 at Anfield to climb two places to eighth.
Teenage winger Raheem Sterling opened the scoring in the 19th minute, galloping onto a pass from Luis Suarez and calmly lobbing the advancing Simon Mignolet.
Suarez added a second in the 26th minute, shrugging off Carlos Cuellar before beating Mignolet at his near post, and the Uruguayan made it 3-0 from Steven Gerrard’s pass seven minutes into the second half.
Suarez’s brace took his tally of league goals to 15, while Liverpool are now only seven points beneath the Champions League places, although fourth-place Chelsea retain a game in hand.
Ahead of the weekend’s FA Cup fixtures, Manchester United lead the table by seven points after winning 4-0 at Wigan Athletic on New Year’s Day, while Manchester City remain second following their 3-0 win at home to Stoke City.