Celtic were unstoppable in the first half and their movement and passing was just too quick and too precise for Rangers, should have scored more.
The only thing that should be a concern for Celtic is that the energy levels dropped in the second half, and even the substitutions did little to reverse that trend. That's not the first time. Makes no difference if the game is won in the first half, of course, but if Celtic go hammer and tongs yet fail to score, then teams might just be able to hold them through the second half. Nonetheless, the pressure is now on Rangers.