The former Manchester United striker appeared to be the target of monkey chants from the home crowd at the Sardegna Arena as he prepared to take the decisive spot kick.

Former Juventus forward Moise Kean was also on the receiving end of racist abuse by Cagliari fans at the same stadium last season.

The 26-year-old Lukaku sent goalkeeper Robin Olsen the wrong way with 20 minutes remaining to mark his second goal in as many games for his new club before turning to glare at the home fans responsible for the taunts.

"I think that in Italy we must improve a lot and be more educated and respectful towards those doing their job," Inter coach Antonio Conte told a news conference.

"In other countries you support the team, you don't insult the opposition like this. There must be the maximum respect.

"Today I was treated well and wasn't insulted, other times it hasn't happened like that and it's not nice."

Romelu Lukaku's penalty helped Inter Milan beat Cagliari. Claudio Villa - Inter/Inter via Getty Images)

Lautaro Martinez had opened the scoring just before the half-hour only for the hosts to level through Joao Pedro soon after the break.

Inter lead Serie A after two rounds on six points along with Torino and champions Juventus, while Cagliari have yet to pick up a point.

The Milan club had got their season off to the perfect start with a 4-0 home win over promoted Lecce, but they struggled to find the same swagger against a Cagliari side featuring former Inter midfielder Radja Nainggolan.

"It was a different game to the win against Lecce, as I had warned everyone this would be tough," Conte added.

"Coming to Cagliari is never a walk in the park. Let it be known, I am very demanding and there is a lot we need to do in order to improve, but I also say we are glad to have won in a difficult arena."

Martinez headed the visitors in front after 27 minutes but his celebrations were cut short by a raised offside flag, although the goal was awarded after a lengthy Video Assistant Referee (VAR) review.

The Sardinian side levelled five minutes into the second half when Pedro powered a header home from a whipped Nahitan Nandez cross.

Stefano Sensi's free-kick rattled the bar for Inter on the hour mark and the midfielder then proved crucial in the winning goal as he was tripped by Fabio Pisacane to hand Lukaku the chance to convert from the penalty spot.

Conte's side welcome Udinese to San Siro in their next league fixture after the international break.