Romelu Lukaku proves the difference again for Chelsea with his fourth goal in four matches as Blues begin their Champions League defence with a narrow win against stubborn Zenit St Petersburg

• Chelsea just about edged the first half but there were no clear chances for either side before the break
• Romelu Lukaku broke the deadlock in the 69th minute when he met Cesar Azpilicueta's cross at the back post
• The visitors came inches from equalising but Artem Dzyuba was unable to turn a low cross on target  

Last season, when they won the Champions League, Chelsea were deemed to have the best overall player in the competition, the best midfielder, the best goalkeeper and the best coach.

This season, as they set out to defend the title, they have Romelu Lukaku. And quite an acquisition he is proving to be. Just four games into the second coming and Lukaku has silenced any doubters and he is stealing the show.

One goal against Arsenal, his first for the club, two against Aston Villa, his first at Stamford Bridge, and then this, his first in Europe for the Blues, the only goal on an arduous night when Thomas Tuchel's team toiled against Zenit St Petersburg.

Little over 20 minutes remained when Cesar Azpilicueta shaped in a splendid cross and Lukaku assessed the flight of the ball, adjusted his feet, sprang high above his marker and aimed his header down powerfully, inside the post.

'An excellent header,' agreed Tuchel. 'That's why he's here. He likes to score and he was again decisive for us, which is great. 

'We did not create many chances for him but he is a guy who brings confidence and belief, and takes pressure from the shoulders of others around him.

'You do not find many strikers of this quality. Goals change the whole momentum of the match.'

The guarantee you might expect for £97.5million, perhaps. One chance, one goal, a lethal strike, the killer touch to turn one point into three just as the celebratory air at Stamford Bridge was fizzling into an anxious hush.

With Juventus in Turin next, it was important for Chelsea to take maximum points in their opener and such a positive outcome seemed unlikely at times in the first half.

UEFA president Aleksander Ceferin appeared on the pitch before kick-off to hand out prizes to Jorginho (best player), N'Golo Kante (best midfielder), Edouard Mendy (best 'keeper) and Tuchel (best coach).

But Chelsea made a sluggish start as the Russian champions flexed their usual formation to mirror Tuchel's back-three, with holding midfielder Wilmar Barrios deployed as one of three central defenders.

They snapped into tackles and broke quickly on the turnover with Brazilians Claudinho and Malcom trying to spring forward in support of lone striker Sardar Azmoun from their positions out wide.

But for all their promise they were able to create very little and Chelsea assumed control in midfield as half time approached and, after the interval, moved the ball around at a brisker tempo, and the visitors retreated. 

Tuchel cut an agitated figure on the touchline, spinning on his heel in frustration and trading thoughts with his coaching staff, just as he had done for long parts of the win against Aston Villa on Saturday.

But he insisted he was content with his team's display, saying: 'We had to work really hard but I felt a huge intensity from us against a very strong opponent with very good players.

'It was tough for us in the first half to find a way of accelerating the game and be dangerous and create touches in the box. We had to be very focused and aware because they have a lot of individual quality up front. We did all that.

'With time it got a bit easier, we played better and it was hard for them to constantly defend spaces. It was a deserved win.'

Antonio Rudiger stirred the atmosphere, soon after the interval, with a careering run from deep inside his own half, slicing through the centre of the pitch, cutting past two Zenit defenders onto going for goal.

Rudiger caught it sweetly and his fierce strike flashed narrowly wide and slammed into the advertising boards but supporters were brought to their feet, roaring their team on.

'Sometimes you need stuff like this,' said Tuchel. 'It was not too crazy but suddenly the gap opened and he tried to finish it himself.'

Moments later, Rudiger swooped at the other end to stop the threat of Azmoun on the break and celebrated his successful challenge with an index finger raised into the air. Again the home crowd rose in response.

Tuchel made his first change soon after the hour. On went Kai Havertz, goal hero on that night in Porto, and Zenit sank ever deeper, until the resistance was broken from Azpilicueta's cross. 'A beautiful ball,' said Lukaku. 'I just had to get my timing right.'

There was a late scare for Chelsea when substitute Artem Dzyuba almost converted a low cross at the back post and crashed into 'keeper Mendy.

But the champions escaped. They start their defence with a win. Lukaku goes from strength to strength.

Scroll down to see how the evening's Champions League action unfolded...