The midfielder concedes that Wednesday's 90 minutes took a huge toll on everyone involved, both physically and mentally.
But, after slipping to fifth place in the championship following the loss to St Johnstone last weekend, Commons and his team-mates accept they have to get their domestic form back on track.
Tomorrow's game against bottom club Dundee is followed by a League Cup tie against Raith Rovers, also at Parkhead.
Commons accepts that a repeat of the Perth performance is simply not permissible and said: "We let a lot of people down. Fans come to watch Celtic and expect a standard of performance, and we never put that in.
"So there was disappointment and anger as we had not done our jobs properly.
"We need to get back to the basics and do the things we were really good at last year that allowed us to go on a winning streak."
The much-hyped opening group stage game against Benfica was given as a reason for the poor display at Perth last weekend, which saw Celtic lose 2-1 after Commons had given them a third-minute lead.
But manager Neil Lennon has made it clear all their focus must now be on tomorrow's game to ensure they do not lose any more ground in the title race.
Commons recognises the importance of regaining momentum ahead of a hectic schedule, which includes trips to Moscow and Barcelona.
He said: "It's a big month and we need everyone fit and focused on the job in hand."
Lennon is demanding that the Champions League is pushed from their minds for now, but Commons believes there will be a positive bounce to be gained from their first match at group stage level for four years.
He said: "I think we have shown we are more than capable of playing in this competition."
Meanwhile, Benfica have launched a bizarre attack on referee Nicola Rizzoli, claiming they were duped out of a "deserved" win.
A statement on their website read: "Benfica had to fight against injustice after injustice.
"Benfica were brave and patient, were the better team and deserved to win on Scottish soil where the Reds had never won.
"The final whistle penalised the best team which was ours! The players could come away with pride."