Pierre-Emerick Aubameyang scored the opener after just five minutes, with Ainsley Maitland-Niles striking sooner after to claim his second Arsenal goal.
Aubameyang made it 3-0 just as nerves were starting to jangle at the Emirates, finishing off a fine move to put the Gunners ahead on aggregate for the first time in the tie as Emery continued his bid to win the trophy for a fourth time.
Pierre-Emerick Aubameyang opened the scoring in the fifth minute then crossed for Ainsley Maitland-Niles to level the tie on aggregate, the Gabon global later scoring a second-half clincher. Sead Kolasinac was aware of that danger, emphatically blocking the risky Sarr well, prompting one of the loudest cheers of the evening.More news: Elon Musk Delivers A Speech To SEC
Rennes picked up four bookings as they failed to answer Arsenal's attacking play, and Aubameyang revealed that their opponents were nervous.
For their part, Rennes grew into the match a little more following a sluggish start and tested Petr Cech before half time through a long-range strike from Hatem Ben Arfa. "There's a long way to go but with performances like that, we can compete".More news: Robert Lewandowski: Bayern Munich didn't take enough risks against Liverpool
Mkhitaryan slotted the ball down the left to Kolasinac, who in turn set up Aubameyang in front of goal for another simple finish.
Arsenal have missed out on Champions League football for the last two seasons, and their poor away record remains a big concerns.More news: Facebook, Instagram down Wednesday: Facebook blames server configuration for longest-ever outage