Forrest took his Celtic tally to 100 goals as he scored three times in his first start of the season.
David Marshall was gifted his second goal when he fumbled a routine shot.
Giorgos Giakoumakis hit in a double in the second half.
In the dying moments, Daizen Maeda made it six to the rampant hosts.
Forrest has not been used much this season but took his chance with both hands, as manager Ange Postecoglou was already missing Jota and decided to rest his squad.
He struck first on nine minutes when he volleyed in a lovely cross from Saed Haksabanovic.
Haksabanovic tore past Chris Cadden and caused a lot of problems for the visitors.
On the left, Hibs were exposed again when Bernabei galloped forward to drill in an inch-perfect pass for Giakoumakis.
Marshall was able to get a shot from Forrest a few minutes later, but then he let another slip past him.
Haksabanovic's cross eventually reached Forrest at the edge of the box. The strike was straight at Marshall but the Hibs captain fumbled the ball over the line before batting it away. The goalkeeper made a terrible mistake.
Four changes were made for the second half after Hibs made it to the interval.
Youan ran on to a Martin Boyle pass to beat Joe Hart, but the comeback was short-lived.
Forrest completed his hat-trick with a shot that went into the corner of the net after Nohan Kenneh's poor kick.
Hibs continued to leave huge gaps for Celtic to exploit, even though the shot was inches away.
The Greek forward's shot from 16 yards was taken away from him by a block from Bushiri as Abada picked out Giakoumakis with a cut-back.
Marshall denied Abada in a one-on-one situation but Celtic would not be denied a late sixth as a cross from the right dropped for Maeda to poke the ball home.
Celtic likes to attack down the flanks and they did just that against Hibs.
Haksabanovic ran riot on the left throughout the first half as Forrest and Abada took on that task from the right during the second half.
Forrest will get the headlines but Giakoumakis was making the most of a rare start and helping himself to a double.
The Hibs full-backs had no protection from the people in front of them.
Lee Johnson's side were lucky to only trail by three at the half because they were careless with the ball and disorganized. Marshall made a howler in the first half and Kenneh made a mistake after grabbing a goal.
The whole group was great, that's what the boss said. That was what the guys who came in gave us.
The goals would come if we played like we did on Wednesday. Some of the comments made about the league were ridiculous. We set out to play a certain way and have fallen short in some areas, but it's not because of a failure of will or effort.
The players wanted to show that we won't change our approach.
"Celtic were very good but we made horrendous errors for all of the goals," said Lee Johnson.
If you can't defend properly, you're going to come unstuck. It's going to be a difficult week for us because we cannot accept that standard.
We have to learn from games like this, whether that's myself and the way we recruit, but also for players to step into these games and not show the fear we showed in the first half.
What are you going to do next?
The League Cup game between Motherwell and Celtic will be played on Wednesday. The first league match to feature VAR will take place on Friday at Hibs' home stadium.
All Rights Reserved © 2024
