The former Wolves striker was one of four changes to the Norwegian's starting XI and was still watching from the bench as Killie defender Darryl Westlake stunned the home support in the 50th minute when he put the Ayrshire men ahead with a deflected drive.
Midfielder Kris Commons levelled eight minutes later and Griffiths immediately replaced James Forrest before notching three goals in a remarkable 19-minute spell to increase the Hoops' advantage at the top of the Scottish Premiership over Aberdeen to eight points with six games left.
Deila, with a joking reference to Griffiths being captured by television cameras eating a cake while sitting on the bench at St Mirren last week, said: "He was fabulous
You can't do better than three goals and his contribution was excellent
He could be a kicker in American football, I think
"He has improved a lot
He is training well and as a 24-hour athlete he is getting better and better - even though he eats cakes on the bench sometimes.
"But still it is just a start and we will continue working on small things to get him better and we will get even more goals."
Deila acknowledged Griffiths looked as if he went onto the pitch with a point to prove to the Celtic boss, who has tinkered with his forward players all season.
He said: "It looks like that, and that is how you do it
That's what you expect from the other subs as well
"You can be angry, but the only way to get back into the team is to really prove that you deserve to play like Leigh did today."
While turning his attention to the William Hill Scottish Cup semi-final against Inverness at Hampden Park on Sunday, Deila is looking to get the title wrapped up "as early as possible".
The former Stromsgodset coach said: "Today was a very important win and we are into a very important week.
"If we can get into the last five games eight points ahead at least we have a very good chance.
Ninth-placed Kilmarnock have now lost four games in succession and remain seven points ahead of Motherwell, who occupy the relegation play-off spot.
However, manager Gary Locke fancies his chances against teams in the bottom six after the split.
He said: "We have to look at the positives
We contained them for long spells and I thought we played reasonably well.
"Our season is not going to hinge on Celtic at Parkhead.
"We have five big games coming up and we have to make sure we win a few of them."
Source : PA
Source: PA