Romelu Lukaku's winner showed why Chelsea signed him, according to Thomas Tuchel after his side defeated Zenit 1-0 in their Champions League opener.

Lukaku's first European goal for the Blues proved the difference as they made it 12 group-stage games without defeat on Tuesday.

The Belgium forward now has four goals in three games against Russian opponents and only Robert Lewandowski, Erling Haaland and Bruno Fernandes have scored more than Lukaku's 14 European goals since the start of 2019-20 when he signed for Inter.

Tuchel splashed a club-record fee on the former Manchester United striker but he insisted that performances like this outing justify the transfer.

"It was an excellent header [from Lukaku for the goal], a well-timed cross by [Cesar] Azpilicueta," Tuchel told BT Sport post-match.

"He was brave enough to step up and we had bodies in the box. That's why he [Lukaku] is here. He likes to score and he's decisive for us."

In the history of the competition, only on two out of 28 occasions have the reigning champions lost the opener and no title defender has ever been beaten at home in their first group-stage tie.

Only Manchester City (11) have won more Champions League matches than Chelsea (10) since the start of last season and Tuchel was happy with his side's start to Group H.

"We had to be at our top level," the head coach continued. "I am happy because we had to work a lot. It was not easy. It's tough to perform consistently at that level.

"We expected a tough game because it's the highest competition in Europe and it's the Russian champions. It took us a while to make them tired but I liked what I saw.

"Winning is good for our belief. We are not finished but we are in a good place to improve.

"The first step is done. But there are five more matches to go [in the group stage]."