Cagliari brought Inter Milan's eight-game winning streak to an end as the Serie A champions struggled to blow away the cobwebs in their first game back after the winter break.
Zlatan Ibrahimovic levelled 12 minutes from time to preserve Inter's unbeaten home record this season after Robert Acquafresca had stunned the San Siro midway through the second half.
Jose Mourinho's men had looked unstoppable in the two months before the three-week break, but never got into their stride tonight and only two glaring misses from Davide Biondini and Acquafresca spared their blushes.
Inter's lead could be cut to four points if Juventus see off Siena tomorrow.
The home side started positively, Maxwell testing Cagliari goalkeeper Federico Marchetti from outside the area and Cristian Chivu shooting wide after being set up by Ibrahimovic early on.
The Sweden striker, played in by Julio Cruz's through-ball, then fired to close to Marchetti, taking his shot early when he had time to steady himself.
Inter survived a scare in the 15th minute, though, when Biondini's sliding tackle on Chivu on the left side of the Inter area, which looked to have given Jeda a great chance to open the scoring, was harshly ruled a foul.
At the other end Cruz could not capitalise on being incorrectly given onside and directed his header from a free-kick wastefully off target.
Marchetti continued to frustrate the home side with another fine save, this time pushing Javier Zanetti's 25-yard effort away for a corner.
Cagliari's season going into the game had been undermined by some woeful form away from home where they had lost six of their eight matches.
But they might have snatched a shock lead a minute before half-time after Acquafresca turned quickly in the area only to see his shot deflected away by Ivan Cordoba.
That chance seemed to encourage the visitors, who showed more adventure after the break and were rewarded with the opening goal in the 65th minute.
Having had a let-off when Ibrahimovic missed from close range following great work from Luis Figo and Zanetti, Acquafresca pounced on a mistake by Walter Samuel and beat Julio Cesar from the edge of the area.
Mourinho threw on Hernan Crespo in place of the Argentinian defender three minutes later in a bid to get his side back into the game, but they should have been dead and buried moments later.
Jeda battled past two opponents before setting up Biondini, who, with time and space inside the area, shot wide of the left post.
And that miss proved costly when Ibrahimovic leveled in the 78th minute, Crespo wriggling free on the left and crossing low for his strike partner to tap the ball home at the far post.
Acquafresca then marred his performance with the worst miss of the night in the 83rd minute, lifting the ball over the bar with the goal at his mercy after Julio Cesar had deflected Andrea Cossu's shot into his path.
The midfielder's embarrassment was almost compounded when Inter substitute Alessandro Mancini tapped home Figo's cross in stoppage time, but the effort was ruled out for offside as the Nerazzurri started the year with a stutter.
