Hibernian 2-0 Celtic:Artur Boruc's blunder blew the title race wide open as Celtic emphatically failed to record a 13th successive Clydesdale Bank Premier League victory.
A tight game at Easter Road burst into life 10 minutes into the second half when John Rankin's speculative effort from 45 yards slipped out of Boruc's grasp and into the net.
Celtic raised the tempo but Colin Nish sealed Hibernian's victory following a slick break in the 69th minute.
Boruc also endured a disastrous afternoon when Celtic lost 3-2 at Easter Road last season - but his poor display that day was seen as an aberration.
This season the Poland goalkeeper has made a series of errors - he was culpable for two goals when Celtic last failed to win an SPL match, against Rangers in August.
Celtic in general were off colour as they failed to find their attacking flow or extend their four-point lead over Rangers.
Gordon Strachan sprang a surprise by naming Shunsuke Nakamura and Georgios Samaras on the bench as Glenn Loovens and Cillian Sheridan came in.
That meant a midfield role for Gary Caldwell while Mark Wilson returned to fitness to replace the injured Barry Robson at left-back. Hibernian also made three changes with former Celt Derek Riordan making way for Nish, while Steven Thicot and Alan O'Brien came into midfield.
Thicot and Shaun Maloney had long-range efforts comfortably saved in the early stages, but the first quarter was devoid of goalmouth action.
Celtic were edging possession and Paul Hartley saw another long-range effort deflected wide but the Hibs central defence dominated in the air.
Celtic were lacking an outlet in right midfield as Scott Brown drifted inside but Maloney set up a chance from the opposite flank when his low cross found Sheridan, only for Ian Murray to produce a great block.
Hibs created their first chance in the 29th minute but Steven Fletcher was off
target after rounding Boruc outside the box.
Rankin had played a superb ball over the top after a tidy piece of skill on the right, but Fletcher was forced wide by Boruc and he shot high and wide as a defender ran back to cover.
The home side pushed forward for a good spell but Celtic soon hit back.
Mark Wilson's cross flashed across the six-yard box after Scott McDonald failed to get enough weight on his near-post flick. Rob Jones then slid in on Maloney inside the penalty area to stop the Celtic winger finishing off a mazy run.
The second half began in similarly low-key fashion. Maloney shot two yards over from long range after a good break by Wilson and Caldwell was booked for fouling Rankin twice as he broke forward.
But the match exploded into life when Rankin's ambitious 45-yard strike somehow bounced underneath the grasp of Boruc and into the net.
Celtic tried to respond and McDonald headed over from a right-wing cross by Samaras, who had replaced Sheridan just before the goal.
Andreas Hinkel shot inches wide after beating two Hibs players to the ball just inside the box.
Boruc, ridiculed at every opportunity by the home fans, caught Rankin's 30-yard strike before Celtic resumed their attacks.
The Hibs defence coped well with several corners and Ma-Kalambay did well to tip Maloney's curling effort wide.
And the home side went two ahead in the 69th minute when Nish scored from close range.
Fletcher released O'Brien through the left channel, he rounded Boruc before pulling the ball back to the far post where Rankin's volley was diverted past the Celtic keeper by the big striker.
Celtic again pushed forward but they were already looking like a beaten team.
Ma-Kalambay saved comfortably from a Samaras header and McDonald could not turn Hinkel's low cross beyond the near post.
Aiden McGeady came on for Hartley and Celtic soon survived a penalty claim when Craig Thomson waved play on as Loovens bundled into Nish.
The Republic of Ireland winger, back after a five-week absence, fired just over from 25 yards and Hibs comfortably held out for their first home win for almost three months.
