Hundreds of fans stood and cheered as the first part of Harry Potter and the Cursed Child came to a dramatic close at London's Palace Theatre.
Throughout the show there had been gasps at the various plot revelations and stage illusions.
As the 1,500 audience members left the show they were given badges asking them to "keep the secrets".
Earlier they had queued around the block - many dressed as witches and wizards - as they waited to clear the strict security in place at the theatre.
The Cursed Child plot digs deep into the world presented in the Potter novels and involves an artefact from Harry's past.
One minor glitch during the first preview involved an owl flying around the auditorium after it failed to return to its handler.
Speaking to the BBC after the show, audience members said the first part of the play had surpassed their expectations.
Raam Suresh, a student in London from Singapore, said: "I can't wait for the next one. I'm hoping it's the first of many more."
Katie Bitter, from Washington DC, said: "I was a little worried it wouldn't meet my high expectations but tonight was absolutely amazing. It didn't feel like a preview at all."
J.K. Rowling Takes Fans Inside The Harry Potter And The Cursed Child Rehearsal Room
Natalie from Ohio said: "I really liked the character of Scorpius Malfoy and seeing Harry, Ron and Hermione grown up. I think they did the magic on stage really well."
Audience member Julia, from Milan, added: "It was really cool. I wish they would do all seven books in the theatre."
Although not an official reviews night, several papers have published their verdict on the first preview.
The Telegraph's Hannah Furness said: "The audience came wanting magic and they got in spades."
The Mirror's Clare Fitzsimons said: "Spells and hexes combined with laughs and drama mean Harry Potter and the Cursed Child will be every bit the hit everyone expects."
The New York Times added: "The three main characters remained true to their younger selves... The audience cannot be more thrilled or more appreciative or more ready to be caught up in the spirit of the undertaking."
Tuesday night's preview marked the first time a Harry Potter story has been presented on stage.
Part two will get its first outing on Thursday night. The show does not have its official opening until 30 July.
The play, written by Jack Thorne and directed by John Tiffany, is set 19 years after the seventh and final book in the series by JK Rowling.
Picking up from where the Deathly Hallows epilogue left off, it portrays Harry, played by Jamie Parker, as an "over-worked" employee at the Ministry of Magic.
His youngest son Albus (Sam Clemmett) has to deal with the "heavy burden" of the Potter family legacy.
Other characters include Hermione Granger (Noma Dumezweni), Ron Weasley (Paul Thornley), their daughter Rose (Cherrelle Skeete), Ginny Potter (Poppy Miller) and Draco Malfoy (Alex Price).
Earlier, Rowling had tweeted a good luck message to Anthony Boyle, who plays Draco's son, Scorpius.
When tickets went on sale last October the first 175,000 sold within 24 hours. The script is already topping bestseller lists, although it will not be published until after the play's official opening on 30 July.
The Harry Potter books have sold more than 450 million copies since 1997 and been adapted into eight films.