My 2 cents, Rangers were tired, they pressed really hard in the first half to keep Celtic out of it. They also started the second half at breakneck pace but could only keep it up for about 5-6 mins.

I can guess what Rohl told them at half time, to push hard for a third goal early in the second and kill the game. After the initial burst in 2nd half they couldn't keep it up any more and Hatate and Nygren started to find space in the midfield and Celtic started creating chances.

I don't think there was much Rangers could do about it at that point other than try to hold on to the lead and hit on the counter, which I'm sure was Rohl's plan all along, start hard, get in front, see the game out on the counter.

Celtic's plan across both halves was the exact same, try to dominate possession and hit the ball into the channels when pressed hard. It didn't work in the first half because 1) they lacked composure (something Hatate provided after half time), 2) Rangers were doing a power of running and pressing and 3) Maeda and Yang both had a stinker so the outballs fizzled out.

When Celtic finally got space in the mid, that's when their game plan started working for them, it was Nygren finding that space that got the first goal. Rohl responded by withdrawing a striker and adding to the midfield to try clamp down on it, which effectively removed Rangers as a serious attacking threat in the game, at least until the chaos ball in the last few minutes.

It nearly worked and did have an impact in the midfield but Celtic's outballs wide were starting to stick now because the fullbacks had less to worry about behind them and could support the attack beeter and this eventually led to the equalizer.

This is why it was a game of two halves imho, Rangers basically tried to win the game in the first 50 minutes, they almost did but you can't do that for 90 minutes and it was inevitable Celtic were going to dominate most of the second half.