To celebrate the film's 80th anniversary, Holly was seen dressed as Dorothy, compete with red slippers and Toto.
She flew into the studio in the back of a London taxi that had been caught in a tornado.
Phil, meanwhile, had spent hours in make-up, having prostethics applied to make him look like the film's Scarecrow.
After Holly untied Phil from his post, he harked back to his musical theatre days and burst into song, which also saw the presenters dance.
This is quite embarrassing and creepy at the same time.
After a performance from an ensemble cast that included Dr Ranj, they headed off down the Yellow Brick Road to find the real This Morning studios.
However, while some fans loved the show's opening, others branded it as nothing more than a "filler show".
Others said it made them "cringe".
So today's show is a filler show , more filler than normal #ThisMorning
— evil batman returns Esq. (@clsyoshimoo) October 31, 2019
#ThisMorning Didn't they do this same thing last year?
— Dave ♿️ Esq (@DaveyBoi73) October 31, 2019
What fresh hell is this? #ThisMorning
— J🇬🇧🇳🇬 (@Artful_Doodler) October 31, 2019
This is quite embarrassing and creepy at the same time.#ThisMorning
— T.H (@NSFtwerk) October 31, 2019
— Becca Lopez (@beccalopezz) October 31, 2019
However, others were full of praise for the presenting pair and their dramatic turn.
Love how this morning go all out for Halloween! #ThisMorning
— beck❄️ (@beckyyalicee_) October 31, 2019
— Shannon (@shanboxoxo) October 31, 2019
— Nick HT Pearmain (@MrNickPearmain) October 31, 2019
— Jules 🦄☕️ (@mejuliejules) October 31, 2019
The costumes were pretty apt for the first segment of the Halloween show, which saw Holly and Phil join a gaggle of witches to cast a spell for snow in London on Christmas Day.
What did you think of the show's opening? Tell us on our Facebook page @EntertainmentDailyFix.