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.
Carpenter 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, so will hope for third time lucky in Lisbon. Caitlin Foord, however, believes Arsenal can deny her the chance.
"I back us to be able to turn it around," said the Gunners' striker.
"We've come from behind before in the Champions League, in the league as well, there's been multiple games where we have done it so the confidence is there.
"Off the back of any loss you just want to get into the game and play again so everyone will be raring to go. We created, we got into the box, we just need to finish it off."
On a north London field far from home Carpenter and Foord spent the afternoon tracking each other's movements, a situation the latter said was unusual.
"I don't think we've played against each other in a competition match before, it's a bit strange, but once you're out on the pitch it's just like any other game."
There was a third Matilda, Steph Catley, nearby at the heart of Arsenal's defence and Kyra Cooney-Cross watching on from their 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 40,000-plus, 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.
"We suffered, but teams that come here will," said Montemurro, "this team has the ability to control the emotion and that's important.
"It's not over yet," he added. "Maybe the pressure is off Arsenal. That's a dangerous scenario and they're a good team."
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.
