The 23-year-old striker, who left Lyon for the Spanish capital two years ago, made an instant impact in Tuesday's match at his old stomping ground, Stade Gerland.
Moments after replacing Emmanuel Adebayor in the 64th minute he received a pass from Cristiano Ronaldo and slalomed across the Lyon box before beating goalkeeper -- and France team-mate -- Hugo Lloris with a measured finish.
He thus became the first Real player to score at Lyon in the Champions League, but a late equaliser from Bafetimbi Gomis meant the seven-time French champions preserved their unbeaten record against the Spanish heavyweights.
"I hadn't dreamed of a better return," said Benzema, who will hope to play a decisive role again when Lyon visit Madrid for the return leg on March 16.
"It's the first time I've scored so quickly. I was lucky to score straight away with my first touch.
"I didn't celebrate it because it was against Lyon; my club, where I grew up. But it was a very important goal. It's good to have scored it because Lyon played a very good match."
Benzema's match-changing cameo drew praise from his coach, Jose Mourinho, who was criticised by Real's sporting director, Jorge Valdano, earlier in the season for failing to grant the Frenchman enough playing time.
"He made a good entrance," said Mourinho. "I knew the match would open up after such a tight first half.
"Lyon were relying on Gomis and us on Adebayor, but we knew there would be space in the second half and Benzema capitalised on that space.
"He scored an important goal for us."
Benzema has been unable to nail down a first-team place at Real since his 35-million-euro move from Lyon in the summer of 2009.
The striker has scored just three times in La Liga this season, despite the long-term absence of Real's Argentine striker Gonzalo Higuain with a back complaint.
He has, however, become the attacking focal point of Laurent Blanc's France team, scoring in the recent friendly wins over England and Brazil, and Mourinho said he had been enthused by the striker's progress.
"Benzema is working very hard and he has improved a lot," said Mourinho.
"He can still become a starting player for Real Madrid. We will have three strikers when Higuain comes back, but big teams need big strikers.
"I think Benzema has improved enormously in terms of his attacking and defensive work, his movement and his personality on the pitch.
"I knew the game would be ideal for him to come into and it was the correct decision."
Benzema has previously acknowledged that working with Mourinho has improved him as a player and he said he was pleased to have rewarded his coach's faith.
"I feel really good. I'm in a period where I'm really exploiting my potential," said Benzema.
"I hope it continues. Mourinho congratulated me but we all played a good match and the most important thing is that we managed to score."