A brace form Pierre-Emerick Aubameyang sandwiched by Ainsley Maitland-Niles first goal at home sealed the victory to send Unai Emery's men into quarter-finals of the tournament.
Maitland-Niles was being given plenty of room down the right-hand side and he made the most of that 10 minutes later when heading Aubameyang's cross past Tomas Koubek.
And the Gunners were soon on level terms in the tie, Maitland-Niles arriving at the back post to steer home a downward header from Aubameyang's cross, Rennes having paused for an offside flag that did not come.
A weak Ramsey attempt aside, which was aimed right at Koubek with the midfielder slightly off balance, Arsenal struggled to create any further clear-cut openings in a stop-start first half that contained a number of careless challenges.
The report goes on to say that Under's current valuation would represent 75 per cent of Emery's summer transfer budget.
A buoyed Rennes then hit the post after the restart, Niang beating former Rennes goalkeeper Cech but not the woodwork after Shkodran Mustafi gave the ball away near his own box.
"We are going to think the same before every match". Sead Kolasinac was aware of that danger, emphatically blocking the risky Sarr well, prompting one of the loudest cheers of the evening.
Henrikh Mkhitaryan, who was a doubt before the game, has made it to the bench.
Gabon global Aubameyang is more used to featuring in the Champions League than Europe's second-tier competition, but his early impact with a goal and an assist was decisive for the Gunners.
It did not matter in the end, though, as Rennes failed to find a way through at the other end.