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 kick-off as UEFA coach, goalkeeper and player of the year respectively.
However, Chelsea did not look like the best team in Europe as they laboured 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 pre-season for many of his stars involved at Euro 2020 and the Copa America.
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.
Lukaku showcased his mix of pace, power and precision in front of goal to score his first Stamford Bridge goals for Chelsea against Villa at the weekend.
Zenit had kept the former Inter Milan striker quiet for nearly 70 minutes, but all he needed was one teasing cross from Cesar Azpilicueta to get off the mark in the Champions League for his new club by planting a header past Stanislav Kritsyuk.
Zenit boss Sergei Semak threw on the towering presence of Artem Dzyuba in search of an equaliser and it nearly paid off.
But even the six-foot six-inch (1.97 metre) Russian international couldn’t stretch to get a clean enough contact on Sardar Azmoun’s cross 10 minutes from time and the ball dribbled wide.
