Franck Kessie had touched the ball only five times before Milan fell behind to Inter at San Siro.

The midfielder proclaimed beforehand that the Rossoneri had no reason to be fearful going into the 174th Milan derby in Serie A history. Far from it. "We'll win the derby and return to the top of the table," he told La Gazzetta dello Sport. "We're a group that has grown through difficulty. We believe in the Scudetto."

That pre-match optimism vanished after those first five minutes on Sunday. So, too, did the sense that this Milan really do believe they can end a 10-year wait to win Serie A. With one swing of Romelu Lukaku's left foot – his crossing remains a hugely underappreciated skill – Lautaro Martinez had an easy header and Inter had it all in their hands: the momentum, the match, and the title race.

Inter now lead the standings by four points, with 14 matches to go, after this 3-0 rout. While that hardly seems an unbridgeable gap, the Nerazzurri have for some time looked the strongest contenders: since exiting European competition in December, they have failed to win just five of 17 games in all competitions, while they have only lost once in the league since Milan won the reverse fixture last October.

Sporting director Piero Ausilio has assembled an experienced squad at great expense, with each arrival tailored to Antonio Conte's exacting standards. It took time, and no little public squabbling, but the Inter boss has finally crafted the sort of team that was expected of him: a powerful, purring results machine.

They were in charge from the moment Martinez planted his header past Gianluigi Donnarumma. They tightened up, harried Hakan Calhanoglu, and broke at speed, and it could easily have been 2-0 or 3-0 before half-time. With a little under half an hour left, it was, as Martinez's poacher's finish and Lukaku's awesome run and strike killed the game stone dead.

In many respects, this result should not have come as a shock. Inter are further down the road towards a restoration of past glories, while Milan have been overachieving for the past year. That they came into this contest just a point off the lead was mostly down to a spectacular run that had long surpassed sustainability. They lost twice in Serie A in the whole of 2020, saw a 27-game unbeaten run only ended by champions Juventus last month and reached the halfway stage of the season with 43 points, their best tally in 60 years.

If it's a surprise that Milan have lost four league games already in 2021, it's only because Stefano Pioli has spent much of the past year defying expectations, imbuing players with the sort of confidence that led to Kessie's unfortunate prediction.

Things could have been different here had it not been for a five-minute masterclass from Samir Handanovic, who twice saved implausibly from Zlatan Ibrahimovic and then tipped a Sandro Tonali strike over just after the interval. But for the 36-year-old's heroics, Milan's early second-half pressure may have given Inter a game to chase, instead of giving them the freedom of the final third to pick through on the counter.

So it was that Lukaku's nerve-settling goal was cheered by the Inter bench almost as loudly as a trophy win. The smiles and high-fives followed; Christian Eriksen was positively beaming as he went off after 78 minutes, his transformation from invisible to undroppable now complete. It showed what Inter know to be true: Serie A is their sole remaining commitment this season and it's firmly under their control.