The 2-1 victory was also a triumph for former Arsenal manager, now Lyon boss, Joe Montemurro, the Melburnian tipped to be the next Matildas coach.
Though Arsenal created enough chances to feel they could get a result in the second leg in France next Sunday (0200 28 April AEST) Lyon's lead, attacking panache and experience makes them firm favourites.
That would delay Montemurro taking the Matildas job - if he is offered it, by another week. The French league ends eight days before the European final in Lisbon on 24 May.
On a north London field far from home Matildas teammates Carpenter and Caitlin Foord spent the afternoon tracking each other's movements, with Steph Catley nearby at the heart of Arsenal's defence and Kyra Cooney-Cross watching on from the Gunners' bench.
Arsenal had blown away Real Madrid 3-0 in their quarter-final second leg here, but eight-times winners Lyon were a very different proposition.
Their multi-national collection of stars settled quickly and deserved their 17th-minute lead. Lindsay Heaps (nee Horan) slid a pass behind Catley to Kadidiatou Diani who finished impeccably. She was flagged offside but a VAR checked revealed American defender Emily Fox had played her on.
Both sides hit the bar as the half became more even. Lyon's Haitian striker Melchie Dumornay doing so from range and Alessia Russo heading onto the woodwork from close. In between, Catley blocked a goal-bound Carpenter shot in a rare foray forward by the full-back.
Roared on by another impressive crowd of around 30,000 Arsenal dominated the second half, Foord being denied soon after the break and Beth Mead and Frida Maanum missing good chances.
Fourteen minutes from time the VAR gave Arsenal a lifeline, highlighting Christiane Endler punching Leah Williamson as the goalkeeper attempted to clear a corner.
Mariona Caldentey rolled in the spot-kick, but as Arsenal went for a winner they were exposed at the back and Dumornay lashed in a shot concluding a move began by Carpenter.
The 24-year-old was badly injured early in Lyon's 2022 final win over Barcelona, and on the pitch for all their defeat to the same opposition in last year's final, will hope for third time lucky in Lisbon. Foord and Catley will hope they can overturn the odds and deny her the chance.
The second semi-final is on Sunday (Monday 0200 AEST) with Chelsea, still without Sam Kerr, whose recuperation from her ACL injury is now its 15th month, away to Barcelona.
