Celtic were top of the Premiership at the start of the season but were relegated after a disastrous start.
Their defeat at Hampsey on Saturday means they will not return to the top flight until the end of the campaign.
Manager Neil Lennon said: “We were in a very good position to beat Rangers in the first half and it took a big performance by Rangers to get back into the game.”
But the players were great and we didn’t let up.
We had a few chances but they were good opportunities to score.
“We were very focused on keeping possession and we kept it simple and that’s the way we have to win.”
The win was Celtic’s eighth in nine matches, and their first in the league since September 2014.