The Celtic boss was reacting to the 2-1 win on Saturday afternoon.
The Norwegian was naturally pleased for Celtic to have registered yet another win but was frustrated that the Bhoys were under so much pressure in the closing stages of their victory, while he also felt his side should have taken far more of their chances.
Leigh Griffiths opened the scoring for Celtic, with Stefan Johansen doubling their lead in the second half.
But St Johnstone hit back and the Hoops had to see out the game with just the one-goal lead.
RD on scoring early: "We always go out to play at 100 per cent and we should have scored more goals on the chances we created." (MH)— Celtic Football Club (@celticfc) February 14, 2015
RD: "But I'm happy to have got the three points. It's always tough to come here. They were aggressive, direct and good at set-plays." (MH)— Celtic Football Club (@celticfc) February 14, 2015
When it came to Deila's second-half substitutions, meanwhile, the Norwegian confirmed he took the key attacking trio of Griffiths, Gary Mackay-Steven and Stuart Armstrong off with Thursday's Europa League tie with Inter Milan in mind.
With Scottish Premiership and European ambitions in mind - as well as that of the Scottish knockout tournaments - Deila says he is keen to utilise every member of his squad he can.
RD: "We have to save all the energy we can and use all the players in the squad so that's why we made the subs." (MH)— Celtic Football Club (@celticfc) February 14, 2015
Celtic's 2-1 win takes them six points clear of second-placed Aberdeen at the top of the Scottish Premiership.