The former prime minister of Italy is standing for re-election to that post, with the ballot boxes closing Monday afternoon, and Stephan El Shaarawy would have cheered him with a slick first-half opener, the young striker's 16th league goal of the season.
Milan were four points ahead of their city rivals at that stage and dominating all over the pitch, but a spectacular save b Samir Handanovic from Mario Balotelli kept Inter alive going into the break.
The Nerazzurri then rallied, reeling in a share of fourth place with Lazio as Schelotto made an instant impact from the bench to head home a vital equaliser.
Inter showed promise as the 208th Derby della Madonnina began, with Antonio Cassano surprising Christian Abbiati with a devious shot from close range.
A stumble from a primed El Shaarawy preceded a dangerous move from Rodrigo Palacio at the other end but Philippe Mexes found the crucial block.
That was all Inter had to offer inside 45 minutes. Balotelli fired one warning shot across the bows and then Milan made a clinical breakthrough.
The Rossoneri soon found they had free rein down Inter's right side and a slick team move saw El Shaarawy open the scoring in the 21st minute.
Kevin-Prince Boateng picked out the Italy striker to shrug off his man on the edge of the box and direct a dipping left-footed drive beyond Handanovic, against the crossbar, and in.
Inter's goalkeeper had little say in the opener given the generosity of his defenders but he kept Milan at bay single-handedly four minutes later.
There looked to no stopping a fierce bullet header from Balotelli, but Handanovic got there with his fingertips, pushing the ball against the bar and smothering it as it bounced wildly off his goalline.
Balotelli kicked the upright after sliding in to stud a Mattia De Sciglio cross against a post and Milan's spell of heavy pressure abated.
If Inter were going to respond before the break and against the run of play, then Palacio's tame header was not the answer and they might have lived to regret his miss had Handanovic not come up trumps once again.
A crude foul on Boateng was in prime shooting range for Balotelli and Inter's Slovenian goalkeeper powered across his line to keep the scoreline respectable at the interval.
If Inter coach Andrea Stramaccioni had addressed his porous defence at the break it was not immediately evident as Boateng waltzed into space to volley Riccardo Montolivo's cross at Handanovic.
Sulley Muntari scored in the midweek defeat of Barcelona but his finishing touch on an Ignazio Abate pass would not linger long in the memory.
Abbiati's save from Fredy Guarin's deflected angled shot was memorable, though, and Cassano nearly followed it up as Inter began to play with more conviction.
Antonio Nocerino drove the ball in low to the six-yard box as the hour mark ticked by but Balotelli's shot did more damage to Handanovic's head as the Inter keeper sprawled against the ball.
Stramaccioni has often been criticised for failing to make the right tactical changes at the right time but his introduction of Schelotto for Esteban Cambiasso in the 69th minute paid immediate dividends.
Just three minutes into his second San Siro outing the January signing from Atalanta raced onto Yuto Nagatomo's cross to glance the ball into the bottom corner of Abbiati's net.
Inter were not as keen to push for victory as they were to close Milan out of the game and Palacio climbed up M'Baye Niang with the French substitute lurking.
El Shaarawy saw a volley charged down as the game reached its climax, with Niang unable to beat Handanovic low to his right.
And four minutes of stoppage time gave Palacio time enough to weave into the area, but an alert Mexes denied him the chance to seal a fourth straight derby win for Inter.