The home win takes the Blues level on points with Manchester United, at the top of the early Premier League table.
On his second home debut for the club, Lukaku was clinical to finish after Kovacic’s through ball on 15 minutes and, then after the break, the Croatian midfielder pounced on a poor Tyrone Mings back pass to fire home his own maiden Stamford Bridge goal for Chelsea.
Aston Villa had dominated in between those two goals, forcing Edouard Mendy into a string of first-half saves, while striker Ollie Watkins was denied by a crucial Thiago Silva block, earlier on.
However, after the error by Tyron Mings – the hosts who weren’t at their best – found a measure of control and then Romelu Lukaku stretched their advantage with a brilliant left-foot drive into the top corner in stoppage time (90+4) to double his tally for the Premier League season.
Chelsea’s sketchy first-half display led to debutant Saul Niguez being substituted at half-time, but the Blues maintained their unbeaten start to the season.