“There was a spark, but now we must become dynamite,” said Conte as he begins his campaign to topple eight-time holders Juventus.
Lukaku – a €65-million summer signing from Manchester United – scored the third goal on the hour mark at the San Siro.
A blunder by Lecce goalkeeper Gabriel parried the ball into the path of Lautaro Martinez allowing Lukaku to finish off.
The 26-year-old turned and took a bow in front of the jubilant Inter fans among the 65 000 crowd.
“Lukaku entered the world of Inter in the best way, with great humility,” said Conte. Various bet options are available on site
“He’s a gentle giant, a giant with a smile. He is ready to work for the team. But not only Romelu, Lautaro also played very well.”
Croatian Marcelo Brozovic had opened the scoring after 21 minutes with a powerful strike for his 15th goal in his sixth season with Inter.
Lecce played the last quarter of an hour a man down after Brazilian Diego Farias saw red in his first game for a studs on tackle on his former Cagliari teammate Nicolo Barella.
Juventus beat Parma 1-0, with Napoli edging a seven-goal thriller at Fiorentina 4-3.
“We started off well with the right intensity and desire, respecting the idea of what I wanted,” said Conte.
“Then at 2-0 I didn’t like what I saw from the lads. Too relaxed, losing intensity under pressure.
“Let’s celebrate until midnight, from tomorrow we think of Cagliari, it will be a difficult trip,” he added of next weekend’s game in Sardinia
Conte’s arrival at Chinese-owned Inter has raised expectations of a first Serie A title since 2010.
The former Juventus and Chelsea boss took over from Luciano Spalletti who secured Champions League football with a fourth-place finish last season.
And former Italy boss Conte’s first game was against his hometown club Lecce, the team where he started his playing career, and who are back in Serie A after seven years.
The sideshow surrounding former Inter captain Mauro Icardi continued with the Argentine not named on the bench.
Inter director Giuseppe Marotta insisted there was no room in the club for the forward, with the transfer window closing on September 2.
Icardi has rejected moves away from the San Siro despite being frozen out of the team and stripped of the captain’s armband last season amid a protracted contract dispute.
Icardi’s wife Wanda Nara, who is also his agent, said he wants to remain at Inter and had been told to stay by senior club bosses.