Lily Allen tackled her critics head on as she took to the stage at the Latitude festival.
Allen took the place of Two Door Cinema Club after they pulled out of the event at Henham Park, Suffolk, at the last minute due to illness and headlined a packed main arena on the opening night.
Earlier in the day she said she was "exhausted by nastiness" on the Twitter site after agreeing to take the Irish indie band's place.
For her second track she joked: "Can we do this at such short notice?" before launching into a rendition of the band's hit Something Good Can Work.
Later in the set she performed URL Badman which is directed at internet trolls.
She told the crowd: "I'm sorry I'm not Two Door Cinema Club but I've promised I'll give it my best."
Earlier on the social networking site, she wrote: "I understand that you're disappointed but I don't think that warrants abuse."
Two Door Cinema Club offered support, sending her a message saying: "You have our unequivocal support. You're a greatly talented artist!"
The singer also drew the crowds as she put on a surprise early-evening performance on The Waterfront Stage.
Appearing alongside her husband Sam Cooper, their daughters Ethel Mary and Marnie Rose and father Keith, she said: "I'm really excited to be here."
Wearing a multi-colour kaftan over ripped denim shorts and a white vest top with silver trainers, the left the stage in a gondola after performing the song As Long As I Got You.
As she was brought ashore she slipped on the jetty, before recovering and waving to fans.
Festival organiser Melvin Benn said he was delighted the Sheezus singer had agreed to join the line-up alongside fellow headliners Damon Albarn and The Black Keys.
He put the abuse down to "a number of idiots" saying many of them may not even be Latitude festival-goers.
Mr Benn added: "She's done a fantastic thing in offering to come and play.
"It's a tough thing to find a headline act at the last minute.
"She's not been to Latitude before. I've spoken to her, she's very happy, she's p***** off about the abuse from the Twitter cranks.
"There's certainly a section of the audience she very much appeals to - she's worthy of any stage."
Albarn has been granted an extra 15 minutes for his headline set so a "well-known friend" can join him on stage. Mr Benn refused to comment on who this mystery guest may be.
About 35,000 people are expected to arrive at the arts and music event this weekend as temperatures approach 28C (82.4F).
Latitude is renowned as the most middle-class event on the UK festival circuit and there has been no attempt to play down that reputation.
The event reinforced those credentials by adding morning yoga classes, a knitting circle and an olive bar to the usual eclectic line-up of ballet, literature discussions and performances by the Royal Shakespeare Company.
Other highlights of the day's line-up include Editors, Billy Bragg and Crystal Fighters.