The Scottish champions beat their Scottish Premiership foes 1-0 thanks to a first-half strike from forward Nadir Ciftci.
However, the visitors could have made life far more comfortable had they not spurned a number of glorious opportunities to extend their lead before Motherwell applied late pressure.
With just one goal in it, Celtic faced a nervous last 20 minutes and their performance levels dropped, prompting Delia to admit that his side need to work on their consistency.
"For 70 minutes it was very satisfying but we should've scored more goals and had at least one penalty, maybe two,” the Celtic boss explained.
"We created a lot of chances and had control of the game. We should've been braver on the ball in the last 20 minutes so that we didn't have to stress so much.”
"Our top level is good and we need to keep that consistency for 90 minutes."
It has been a somewhat common theme for Celtic on their travels in the past – dominate the opposition, open the scoring but then inexplicably take their foot off the gas in the latter stages.
Motherwell weren’t too far away from securing an unjust result, and a lack of profligacy is a weakness which needs rectifying if Celtic intend on once again playing at the top level in Europe.
Aberdeen’s third defeat in succession has allowed the Hoops to regain top spot and with two home games in quick succession to come in the league, there is a real opportunity for Delia’s side to start pulling clear.