Lacazette had come off the bench in Arsenal’s previous three games as he returns to fitness.
It came after he missed the recent Premier League victory over Bournemouth having been struggling with a groin injury.
But the Frenchman started in the Europa League and scored the only goal of the game in an Arsenal victory.
It extended the Gunners’ unbeaten run to 22 in all competitions and they top their Europa League group.
And Emery has explained that Lacazette was selected to help him find some form ahead of a busy festive period.
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“First we needed to have the mix of the first XI with young players,” Emery said.
“You can improve, you can play better if you have players who can help you on the pitch.
“For example Sokratis, he cannot play Sunday and he could play today.
“Lacazette, I think he needs rhythm to play and it’s not bad for him to play today.
“We decided for this reason and because every player who played today can play Sunday.”
Arsenal’s win over Qarabag will be remembered more for a return to action of defender Laurent Koscielny.
The centre-back made his first appearance of the season and helped keep a clean sheet.
And former Gunners star Martin Keown expects him to secure his place back in the side.
“Koscielny and Sokratis, is that going to be the partnership now for Arsenal?” Keown said on BT Sport.
“Perhaps long term it could be.
“Koscielny an outstanding player, of course only missed the World Cup really because of that shocking injury that he got in the semi-final of this competition last year.
“He has been back in training for a number of weeks, I think about eight weeks or so.
“They held him back and I’m pretty certain he’ll be ready.”