Inter surrendered a two-goal lead with goalkeeper Samir Handanovic badly at fault as Torino battled from behind to earn a 2-2 draw at San Siro.
First-half goals from Ivan Perisic and Stefan de Vrij seemingly set up victory for Inter and looked to have got Luciano Spalletti's side back on track for a possible Serie A title tilt after they lost 1-0 at Sassuolo on the opening weekend.
Torino improved after the interval and got themselves back in the game in the 55th minute, though, Andrea Belotti finishing off Iago Falque's brilliant long-range pass.
And 13 minutes later Soualiho Meite's deflected shot squirmed away from Handanovic to earn Torino a hard-fought point, which Salvatore Sirigu preserved with a brilliant injury-time save from Perisic.
Inter led within six minutes through an excellent goal, Mauro Icardi pulling back a low cross from near the corner flag with Perisic beating Sirigu with a sweetly struck first-time finish.
Sirigu saved Matteo Politano's header but the goalkeeper was beaten again before the break as De Vrij nodded in his first goal since joining Inter from Serie A rivals Lazio.
Politano provided a dangerous inswinging delivery from a free-kick wide on the right and De Vrij's clever flicked header found the bottom-left corner.
Falque scored in this fixture last season but bent a free-kick just wide on the stroke of half-time.
He got Torino back in the game after the break, though, sending Belotti through with a sensational pass from inside his own half.
The striker's superb first touch outfoxed goalkeeper Handanovic and Belotti was left with the simple task of rolling in his third goal against Inter at San Siro.
Torino were suddenly dominant and Meite skipped away from a sliding challenge to slot home the equaliser, Handanovic's weak right hand only able to push the ball in off the post.
Belotti headed a brilliant chance to win the game wide as Falque again bamboozled the Inter defence, but Perisic almost won it at the death, Sirigu leaping high to his left to deny the Croatian.
What it means: Scudetto hopes already fading for Nerazzurri
Many pundits were backing Inter to provide the strongest competition for Serie A champions Juventus this season, but losing to Sassuolo was a poor start. And giving up a two-goal lead at home to unfancied Torino showed there is still a lot of work to do for Spalletti and his team.
Pat on the back: Falque inspirational in fightback
Falque barely had a kick in the first half but after the interval he hauled Torino into a position where they could easily have won the game. His crossfield 50-yard ball for Belotti's goal is an early contender for pass of the season and he ran Inter ragged in a thrilling second half. Belotti really should have headed home a fantastic Falque cross late on to claim all three points.
Boot up the backside: Handanovic bloopers cost Inter
Inter's goalkeeper has proven himself a more than capable presence over the years but Torino were gifted a route back into the game by Handanovic. Belotti was always going to cut inside onto Falque's long pass and the Slovenia international made himself look silly by trying to cut off the angle but getting his positioning all wrong, leaving the striker an open goal. Torino's equaliser should have been saved by Handanovic once he got a hand to the ball as well.
Inter will seek to find some momentum in their last game before the international break away to Bologna on Saturday, with Torino hosting SPAL the following day.