The two Matildas, so influential for their club sides, were both at the heart of the action in the Parc Olympique Lyonnais as Wednesday's closely contested tie was decided by Guro Reiten's fine 28th-minute winner.
Kerr, feeding largely off scraps amid Chelsea's counter-attacks, still proved hard to handle for the home defence and came close to scoring on several occasions.
Carpenter, getting back to her best after her recovery from the ACL injury suffered in last year's Champions League final that kept her sidelined for nine months, grew increasingly influential after the break, marauding forward from fullback.
But even though Europe's most successful women's team Lyon, who have won the tournament in six of the past seven seasons, hit the woodwork in the second half, it's Chelsea who carry the crucial advantage into next week's return leg at Stamford Bridge.
On course to take a fourth successive Women's Super League title in England following a fine campaign, the Blues are desperately seeking the one major trophy to so far elude them during Kerr's dazzling spell at the club.
They could have enjoyed an even more substantial advantage. After Reiten's curled shot had whipped past Lyon goalkeeper Christiane Endler, Chelsea almost doubled their lead when Lauren James' effort bounced off the post.
Eight-time winners Lyon dominated much of the second period, and came close to an equaliser when Delphine Cascarino's shot struck the woodwork after Chelsea failed to clear their lines.
Chelsea had several chances to put the game, and possibly the tie, to bed but they failed to land a decisive second, with Kerr blasting over with a left-footed drive only for the offside flag to be belatedly and incorrectly raised.
- with PA
