LONDON (Reuters) -Romelu Lukaku opened his Champions League account for Chelsea as his powerful header earned the holders an unconvincing 1-0 victory over Zenit St Petersburg at Stamford Bridge in their Group H opener on Tuesday. Chelsea were hardly convincing, however, and Thomas Tuchel's side did not even manage a shot on target in a pedestrian first half. They did improve in a far more entertaining second period in which Zenit looked capable of springing a surprise. A cagey first half ended with Zenit's keeper Stanislav Kritsyuk not even required to make a save as Chelsea struggled to get the ball to an isolated Lukaku. Kai Havertz, Chelsea's hero from last season's final in Porto, came off the bench in the 63rd minute, replacing Ziyech.
