Ayyoub Bouaddi debuts for Manchester City, but Erling Haaland stars in a 2-0 win in Porto.

Erling Haaland scored twice as Manchester City began their Champions League campaign with a 2-0 victory at Porto.

Haaland was denied by a hat-trick of fine saves by Diogo Costa before half-time, but he was not to be denied early in the second half, as his downward header found the bottom corner.

Porto pushed the English giants back for the rest of the second half but lacked the quality to punish Enzo Maresca’s men despite a series of sloppy errors from the visitors.

Haaland showed the difference in class between the sides when he clinically slotted into the bottom corner in stoppage time to become City’s third-highest goalscorer of all-time on 167 goals.

“We have all the pressure; we have to deliver on the biggest stage, and that’s what we did today,” Haaland told Amazon Prime.

“These are the games you have to win, and we’ve got a great start to the season.

“In the Champions League, you have to win games, because if not, suddenly you get all the pressure, and then you never know what’s going to happen.”

Backed by a record 460 million-pound ($620m) splash on new signings, Maresca has made a positive start to the daunting task of succeeding Pep Guardiola in the City hot-seat.

But Haaland remains the main man for City and has not shown any sign of a hangover from his World Cup heroics with Norway, netting five times in his first four games of the new campaign.

Maresca handed Ayyoub Bouaddi his first start since his 100 million-euro (85.6 million-pound, $117m) move from Lille.

Remarkably, the teenage Moroccan is still only the third most expensive midfielder City signed in the transfer window after Enzo Fernandez and Elliott Anderson both surpassed the 100 million-pound ($135m) mark.

Bouaddi and Fernandez impressed in a bright first-half display from City that only lacked a goal thanks to a masterclass by Costa in the Porto goal.

The Portuguese international flung himself high to his left to claw away a powerful Haaland header with the visitors’ first big chance.

Costa foiled the giant Norwegian once more with a brilliant double save after fine play by Bouaddi and Phil Foden in the build-up.

Porto’s last line of defence was finally breached just two minutes into the second half.

This time, Haaland’s header from Fernandez’s cross had far less power but trickled into the bottom corner with Costa wrong-footed.

Yet the goal provoked a transformation in Porto’s attacking intent, while City were guilty of easing off.

Gianluigi Donnarumma was saved by the offside flag after he raced off his line to wipe out Pepe for what would have been a clear penalty.

That was not the only heart-in-mouth moment for the Italian, as his attempted clearance was charged down by William Gomes but bounced agonisingly wide for the home side.

City also faded badly in the closing stages to just hold on to a 1-0 win over newly-promoted Coventry on Saturday.

This time, though, they got the second goal to kill Porto off as Haaland slotted in Rayan Ait-Nouri’s cross for his 59th Champions League goal in 59 games in the competition.