Striker Michy Batshuayi scored twice to edge Chelsea past a spirited Bristol Rovers and into EFL Cup round three.
The £33m summer signing from Marseille volleyed in, and Victor Moses struck from close range two minutes later.
Peter Hartley halved the lead by heading in a free-kick before Batshuayi restored the hosts’ two-goal cushion.
Ellis Harrison scored a penalty and struck the crossbar for League One Rovers, but Chelsea maintained their 100% record under Antonio Conte.
The Premier League side enjoyed the vast majority of possession in the first half, but were denied by excellent goalkeeping from Steve Mildenhall and wasteful finishing.
Batshuayi, initially guilty, took his tally to three goals in three games courtesy of two smart finishes, with the bright Ruben Loftus-Cheek involved in the build-up to both.
Around 4,000 vocal Rovers fans had plenty to cheer with two goals, in addition to spells in the second half when their side caused problems.
That revival persuaded Conte to send on Eden Hazard, John Terry and Oscar in an attempt to preserve Chelsea’s lead, while Batshuayi was denied a hat-trick in the closing stages by the referee’s assistant’s flag.