If justification were needed for Chelsea’s decision to spend £97 million to bring Romelu Lukaku back to Stamford Bridge, the Belgian provided it with a master striker’s goal on Tuesday.

In their first game in the competition since winning the Champions League against Manchester City in May, Chelsea were being frustrated by a well-drilled Zenit St Petersburg.

With little over 20 minutes remaining Chelsea skipper Cesar Azpilicueta delivered a peach of a cross towards Lukaku and the Belgian speared his header past keeper Stanislav Kritsyuk.

It was Lukaku’s fourth Chelsea goal since joining from Inter Milan and offered further evidence that he could be the key part of manager Thomas Tuchel’s jigsaw this season.

“It was an excellent header, a well-timed cross by Azpilicueta,” said German Tuchel, who has transformed Chelsea since replacing Frank Lampard in January. “That’s why he is here. He likes to score and he’s decisive for us.”

Tuchel can often be an animated figure on the touchline but he was calm throughout Chelsea’s opening Group H clash even when his side were struggling to open up the resolute Russians.

Chelsea did not have a shot on target in the first half but picked up the pace after the break.

“It was not frustrating. It was tough against very strong opponents,” Tuchel said.

“We struggled a bit to create chances and shots in the first half. In the second half it was a bit easier to find spaces and shoot. It was a deserved win. Hard earned. It took us a while to make them tired but I liked what I saw.”

While it was not a dazzling display by Tuchel’s side, it was a 23rd clean sheet since he took charge — more than any other team in Europe’s top five leagues in the same period. And it showed that when they are not firing on all cylinders they can grind out wins — especially with a poacher like Lukaku offering an old-fashioned route to goal. “The performance from Romelu was not easy. He’s the type of guy who doesn’t lose confidence and belief,” Tuchel said.

Allegri happy

Juventus coach Massimiliano Allegri said his side are still trying to find their rhythm and are not doubting themselves despite a rocky start to the season.

Juventus have picked up one point from their first three Serie A games but secured a 3-0 win in their Champions League opener against Malmo on Tuesday, thanks to goals from Paolo Dybala and Alvaro Morata.

Allegri said new signing Manuel Locatelli needed more time to gel with the team, while Rodrigo Bentancur and Adrien Rabiot had yet to hit their stride.

“We cannot allow three negative results to make us doubt this team,” said Allegri, who returned to take charge of Juventus for a second time in May. “A player is not either good or poor just because the team wins or draws.