One split second of madness, an inexcusable rush of blood to the head or uncontrollable reaction can change the course of a game.
Sokratis picked up a yellow card for a clumsy incident in the 33rd minute and within 7 more, the burly Greek went for broke with a 50/50 arm shoving contest with Sarr before taking him out as he approach the Arsenal goal.
In truth, from the moment the first yellow was shown, Sokratis should have taken more care because of what was at stake but in between both cards, he made another questionable attempt to reclaim the ball.
It all looked so good in the early stages and Arsenal were given a dream start.
Just 4 minutes in and Iwobi received a ball from a useful exchange involving Xhaka and Monreal.
He turned and offered a low curling cross, come shot , which deceived everyone and ended up in the back of the net.
However, it was almost inevitable that Sokratis would flirt with danger and get bitten and although the game was still within Arsenal’s control, they managed to continue giving opportunities to the opposition, surrendering space and giving away unnecessary free kicks in key areas in the Arsenal half.
Sokratis departed and the resulting free kick was a shocker, Bourigeaud sent the innocuous effort straight into the wall but it kindly came back at him and he struck it so sweetly that as soon as it left his foot, you assumed it would stretch the net.
The right footed scorcher flew into the top left corner and Cech may have needed to be twice his height to enable him to stretch as far but even then, it may have remained a goal.
At 1-1 it seemed salvageable.
Ozil and Iwobi were finding space and still looked a threat and all they had to do was consolidate and regroup.
My immediate thought was to put Xhaka in the backline, he’d acquitted himself reasonable well before when required.
What I wasn’t prepared for was the sight of Mkhitaryan as a right back and after half time, he was still there.
To me that was an invitation to the opposition to pile forward, turn him inside out and make him spontaneously combust.
That wasn’t the only problem, because Monreal, who had been reasonable for the majority of the first 45 minutes was then exposed for his considerable lack of pace.
This left Koscileny to fight the majority of the fires in and around the Arsenal box and he played his socks off.
Had it not been for Cech and the Arsenal captain’s efforts, the North London club would already be out.
Another goal was almost inevitable and in the 65th minute, Arsenal assisted Rennes in every respect to increase the deficit.
Bensebaini hit a directionless ball forward which it appeared the Arsenal players thought would go out of play.
Not so Zeffane, who
gave chase on a seemingly lost cause, caught up with it and whipped a dangerous looking cross from the right, which deflected off Monreal and past Cech.
Cech was having one of those nights where no matter how good he was, others weren’t and it seemed that bad luck would take matters into its own hands.
The big keeper stood firm and minutes later he denied Ben Arfa after a failed Mustafi clearance.
It arrived at the shot stopper from at least 20 yards out and was destined for the left corner but Cech showed his class with an excellent, sprawling, fingertip save.
Arsenal had been in a generous mood all evening, gifting free kicks all night long, surrendering space with every attack and failing to settle for what they had.
2-1 wouldn’t have been a terrible result considering the one man shortage but Arsenal needed to remind themselves that damage limitation was the priority but the errors continued.
Arsenal were making a hash of this and giving themselves everything to do in the return leg.
Then in the 79th minute, Emery made his last bid to keep things heading in the right direction by replacing an out of salts Aubameyang with Kolasinac but it would count for nothing.
Silicki surged forward and provided the perfect cross for the unmarked Sarr, who steered the ball past Cech.
It was no more than the Rennes player deserved for all his commitment and if Arsenal are looking for new players in the summer, his name would be a useful and welcome addition.
Arsenal know what they have to do, score a minimum of two goals without reply but there will be no Lacazette and no Sokratis, that job suddenly seems more difficult than it did initially.