Romelu Lukaku was decisive off the bench with a late winner as Inter scraped a 1-0 victory over Porto in the first leg of their Champions League last-16 tie at San Siro.

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 then 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.

Martinez would have been frustrated to miss the target with an unchallenged header from Federico Dimarco's 13th-minute cross.

That chance punctuated the largely dull early exchanges, but the contest showed signs of life in the final eight minutes of the half.

Marko Grujic's fierce strike hit Andre Onana's knee and Galeno nodded the follow-up wide, before a remarkable reflex save from Costa kept Bastoni's header out.

Inter then owed a debt of gratitude to Onana just before the hour. He made a fine save to deny Zaidu Sanusi and then somehow kept Mehdi Taremi's rebound out on the line with the Iranian seemingly destined to score.

Otavio's dismissal for a lunge on Hakan Calhanoglu 12 minutes from time gave Inter a numerical advantage, and they duly made the most of it.

Substitute Lukaku headed Nicolo Barella's cross against the post but was on hand to slam the rebound beyond Costa.

What does it mean? Inter go to Portugal with something to protect

This certainly was not a classic and Inter were underwhelming for much of the game. There would have been few arguments about a draw being a fair result.

But Inter finished the match really well and deserve praise for getting the win over the line when they had previously looked unconvincing.

The tie is by no means done, but now Porto have to win the second leg – Inter have only lost one of their past 14 matches across all competitions, so that will be no easy task for Sergio Conceicao's side.

Onana shows his worth

There was a flashpoint in the first half when Onana and Edin Dzeko appeared to be engaged in a heated argument. While it was unclear what that was about, there was little about the goalkeeper's performance that could be criticised.

He made four saves in total, but among them were the fine block from Grujic's piledriver and the double stop to deny Sanusi and Taremi in the second half, the latter essentially denying Porto a certain goal.

Otavio's petulance proves costly

There was no doubt about the booking for his second yellow as Otavio caught Calhanoglu with a nasty challenge.

However, that would not have led to a red had he not made the bizarre decision to rile Inter in the first half. The hosts had put the ball out of play to allow a player to get medical treatment – when Porto restarted with a throw-in, Otavio started darting towards the Inter goal when he knew the protocol was to give possession back.

A melee ensued and he was booked – he must feel a little silly now.

Key Opta Facts

– Inter have won consecutive games in the knockout stages of the Champions League without conceding a goal (1-0 v Liverpool in March 2022 and 1-0 v Porto) – only under Jose Mourinho in 2009-10 had they previously won consecutive knockout stage matches without conceding (a run of three). 
– Porto have failed to progress from six of their previous seven knockout ties in the Champions League when losing the first leg, with their only progression coming against Roma in the round of 16 in 2018-19. 
– Inter have won three consecutive home games in the Champions League for the first time since November 2010 in a run of seven, during which time they lifted the trophy in the 2009-10 campaign.
– Lukaku's strike was the first winning goal scored by a substitute for Inter in a Champions League game since Giampaolo Pazzini in March 2012 (v Marseille, also in the round of 16). 
– Otavio's dismissal was the 22nd red card Porto have been shown in the Champions League, with only Juventus (27) having been handed more. Otavio was the first Portuguese player to be sent off for Porto in the Champions League since Secretario in March 2002 (v Panathinaikos). 

What's next?

These two will tussle again in Porto on March 14.