Fans supported Billie Eilish through her Electric Picnic gig after she complained of feeling “really, really sick” before her performance.
The US superstar, 21, headlined the first day of the Irish event at the Stradbally Estate, Co Laois, on Friday.
Social media videos showed her delivering her Barbie soundtrack hit What Was I Made For? in a white Nike shirt and baseball cap.
She was joined by the crowd who sang along to songs including Happier Than Ever.
Eilish had previously told her followers to help her at the concert.
In an Instagram story, she wrote: “I am really, really sick, and honestly really suffering.
“You know me and you know that I wouldn’t cancel a show even if I was like literally dying… (this does feel pretty close tho lol) but the show must go on.
“I will see you tonight! But please keep in mind that I am trying my best and I’m gonna need your help tonight. Go hard for me.”
One Direction star Niall Horan, who sang Sinead O’Connor’s hit Nothing Compares 2 U in tribute to the late singer, also made reference to his local roots as he delivered an emotional speech at the festival.
The Westmeath-born singer told the crowd: “I wish I could put into words how this felt. From Patrick Street, Mullingar, to this.
“This is a country with less than five million people, and the noise that we make worldwide is insane, and as long as you would like me to, I’m happy to fly the flag for our little country all over the planet.
“I love our little country. I love being here tonight. I love you all. Thank you so much for coming out to see me.
“This is by far the biggest audience I’ve played to as a solo artist and I really appreciate it, the support from my home nation.
“It’s great to be back in the Midlands, only an hour away from home, and have this. Thank you all so much.”