Newcastle United's Papiss Cisse opened the scoring midway through the first half with a ferocious strike
Chelsea's hopes of finishing in the Premier League's top four suffered a hammer blow as Newcastle kept their own challenge for a Champions League place on course with a stunning 2-0 win at Stamford Bridge on Wednesday.
Roberto Di Matteo's side looked drained by their recent gruelling schedule as they delivered a flat performance that was punished by two astonishing goals from Newcastle striker Papiss Demba Cisse.
It was just Chelsea's second defeat in 17 matches under interim manager Di Matteo, but it could prove so costly as the Blues now trail fourth placed Tottenham and fifth placed Newcastle by four points with only two games remaining.
Unless Tottenham and Newcastle fall apart in their final fixtures, Chelsea will need to win the Champions League final against Bayern Munich on May 19 to avoid failing to qualify for Europe's elite club competition for the first time in owner Roman Abramovich's nine-year reign.
For Newcastle, this was the perfect response to Saturday's 4-0 defeat at Wigan and their seventh win in eight matches -- which keeps them level on points with Tottenham -- was just reward for Cisse's superb finishing and a supremely disciplined display.
It will have made uncomfortable viewing for leaders Manchester City, who travel to Newcastle on Sunday in a crucial game for both clubs.
With the FA Cup final against Liverpool looming on Saturday, Di Matteo made six changes to the side that thrashed QPR 6-1, with Frank Lampard, Ashley Cole and Juan Mata joining Didier Drogba on the bench.
Fernando Torres was one of those who kept his place and the Spaniard led Chelsea's early assault on Tim Krul's goal.
Torres's movement and energy threatened to unhinge Newcastle on several occasions and his pace took him clear to whip over a low cross that Daniel Sturridge scuffed wide.
But that failed to rattle Alan Pardew's well-drilled outfit and it soon became clear Chelsea were lacking the relentless aggression which has defined their revival under Di Matteo.
The lethargy that suffocated their performance allowed Newcastle to grow in confidence.
They went close to taking the lead from a well-worked set piece routine that saw Demba Ba hook a bicycle kick over the bar after Mike Williamson headed down Hatem Ben Arfa's free-kick.
Chelsea's defenders were guilty of more slack marking as Senegal striker Cisse opened the scoring in the 19th minute.
Davide Santon was allowed to make a driving run towards the Chelsea penalty area and the defender flicked a pass to Cisse, who had enough time and space to clip the ball into the air with one touch and lash an unstoppable shot past Petr Cech with his second.
It was Cisse's 12th goal in just 12 appearances for the Magpies since his January move from German club Freiburg.
Starved of service, Torres was forced to seek the ball in wider positions and he delivered one teasing cross that Florent Malouda headed just wide.
In Ba, Cisse and Ben Arfa, Newcastle possessed a much more threatening forward line and Ba twice went close to doubling the visitors' lead before the break.
First he tormented Branislav Ivanovic with a surging run and fired in a low shot that Cech pushed away for a corner. And from the resulting set-piece, Ba turned quickly to whip a powerful strike against the bar with Cech beaten.
Newcastle suffered a blow midway through the second half when midfielder Cheick Tiote was stretchered off after lengthy treatment following an aerial clash with John Obi Mikel.
But the closest they came to an equaliser was John Terry's glancing header from substitute Mata's corner that was superbly cleared off the line by Santon.
It was Cisse who delivered the killer blow in the third of 10 minutes stoppage time when he took aim from way out on the left and arrowed an incredible looping shot over Cech into the far corner to seal the points.