South Korean international Oh was handed a rare start with Kyogo Furuhashi left on the bench by Brendan Rodgers.
And he took his opportunity as Celtic remained unbeaten in the league this season.
"He works ever so hard at his game so he's ready when he comes on," said Rodgers.
"I was very, very pleased for him. He's taken his goals really well."
Oh deflected in Cameron Carter-Vickers shot to open the floodgates after just five minutes.
Hibs had held the Scottish champions when the sides met in Edinburgh in October, but there was little hope for the visitors once Matt O'Riley made it 2-0 midway through the first half.
Luis Palma's penalty and a classy finish from Oh put the outcome beyond doubt early in the second period.
Christian Doidge grabbed a consolation for the visitors, who remain in fifth.
The in-form Abdallah Sima was Rangers' hero at Tynecastle as Philippe Clement's men kept the pressure on their Glasgow rivals at the top of the table.
The Brighton loanee latched onto James Tavernier's through ball and coolly chipped Zander Clark for the only goal on 34 minutes for his 12th goal of the season.
But Rangers were thankful to a fine save from Jack Butland made a fantastic save from Kenneth Vargas late on to secure all three points.
Aberdeen slipped to second bottom after a 1-0 home defeat to Kilmarnock.
Chris Kane's injury-time winner moved St Johnstone out of the bottom two with a 1-0 victory over St Mirren.
