Romelu Lukaku (right) of Chelsea scores against Zenit Saint Petersburg on Tuesday in London, England. Photo: VCG

Chelsea manager Thomas Tuchel said Romelu Lukaku's knack of scoring decisive goals is what the Blues were missing despite winning the Champions League last season.

Lukaku enlivened an otherwise flat performance with the only goal to beat Zenit Saint Petersburg 1-0 on Tuesday to get the Blues' defense of their ­European crown off to a winning start.

The Belgian striker now has four goals in as many games since returning to the club for a club record 97 million pound ($134 million) last month.

And his predatory instincts 21 minutes from time papered over the cracks of a disappointing display from Tuchel's men.

"He was the type of guy we were missing," said Tuchel. "It is super hard and super important. You don't find many strikers of that quality.

"The guys who are there to score regularly for their teams are so important because one goal changes the whole momentum of the match.

"The performance for Romelu was not easy. We did not create many chances for him, but he does not lose confidence and belief. That's why he's here and why he's a world-class striker."

Tuchel urged his players not to rest on their laurels after their surprise run to become European champions last season.

The glory of their victory over Manchester City in Porto was hard to shrug off as the German, Edouard Mendy and Jorginho were presented with awards on the pitch before kickoff as UEFA coach, goalkeeper and player of the year respectively.

However, Chelsea did not look like the best team in Europe as they labored to create chances against the Russian champions.

"There are a lot of reasons why we are maybe not on the highest level at the moment," added Tuchel, citing a lack of preseason for many of his stars involved at Euro 2020 and the Copa America.

"I'm happy with how we play because I find us very competitive and we know how to handle difficulties during matches."

A remarkable run of 23 clean sheets in 36 games under Tuchel has been the bedrock of Chelsea's success since he took charge in January and was again needed to grind out three points.

The first half came and went without the home side even registering a shot on target.