Flamboyant dance routines and a lively performance of their new single Gentleman met an enthusiastic reception in Londonderry.
The festival is being held at the former Ebrington army barracks in the city to coincide with its year as City of Culture.
Thousands of people will attend the three-day long show which kicked off on Friday with performers including Calvin Harris.
Scottish rock trio Biffy Clyro are Saturday's headliners on the main stage, dramatically framed by the city's church spires and riverscape along with the serpentine Peace Bridge, opened to symbolise the city's efforts to bridge the gap between nationalists and unionists.
Vocalist Simon Neil said: "This venue is a spectacular place.
"It is just such a beautiful part of the world and great to be part of the City of Culture and for Radio 1 to host.
"This is an amazing event."
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