The Bhoys were favourites to win the encounter at McDiarmid Park in Perth, but the match ended in a goalless draw.
“I think it was an even game,” Deila told BT Sport after the match. “I think a draw is okay, but it was 0-0. That was a miracle.”
Although the game finished in a goalless draw, both sides had chances and could have scored.
Over the course of the 90 minutes, visiting Celtic had 46% of the possession, took 12 shots of which four were on target, and earned seven corners.
Hosts St Johnstone had 54% of the possession, took 16 shots of which seven were on target, and earned 11 corners.
Celtic, who have already won the Scottish Premiership title this season, now have 89 points from 37 matches.
Meanwhile, St Johnstone are fourth in the standings at the moment with 54 points from 37 games.
Celtic are back in action next weekend, when they take on Inverness Caledonian Thistle at Celtic Park in the Premiership.