Hosted by the hilarious Catherine Tate and presented with Mastercard, this year's Olivier Awards ceremony included performances and presentations from the likes of Chita Rivera, Cuba Gooding Jr., Patti LuPone, Michael Sheen, and Andrew Lloyd Webber.
Sir Peter, founder of the Royal Shakespeare Company and director of the National Theatre, died aged 86, in September.
The failure to mark his death prompted dismay and disbelief on social media.
Olivier Awards 2018: What else happened?
In a statement on Twitter, the Olivier Awards said: "We are hugely sorry for the oversight of leaving Sir Peter Hall out of our In Memoriam during last night's Olivier Awards".
Film actor Sir Roger Moore, US pop star David Cassidy and RSC co-founder John Barton were among those whose names and faces were projected on a screen.
In her acceptance speech, Atim said: "I want to acknowledge some of the women who have been on this stage before me - Noma Dumezweni and Amber Riley, because they've been here accepting awards, and they look a bit like me".
Yet there was no mention of Sir Peter Hall - a man SOLT called "a peerless British director and theatre impresario" when he died past year. It dimmed the lights for a minute in West End theatres as a mark of respect.
The musical, which won 11 Tony Awards in the United States in 2016, picked up seven Olivier Awards in London on Sunday. Lesley was nominated for Best Actress for her part in Long Day's Journey Into Night, but lost out to Laura Donnelly for her role in The Ferryman.
The award for Best Actor in a Play went to Bryan Cranston for Network and Best Supporting Actor went to Bertie Carvel for Ink.