Simone Inzaghi's men appeared to be heading for a disappointing goalless draw that would have arguably put Porto in the driving seat for the second leg, but Lukaku came to Inter's rescue.

The Nerazzurri had been wasteful during a tense first half, with Lautaro Martinez spurning a great opportunity and Alessandro Bastoni forcing Diogo Costa into a brilliant save.

They it struggled to make the most of their dominance in the second half, but shortly after Porto midfielder Otavio was sent off, Lukaku turned home to score for the second time in less than a week.