Hollywood actor Will Smith surprised the crowds at T in the Park by introducing headline act Calvin Harris.
The Men In Black star took to the main stage before the DJ appeared in front of tens of thousands of people at Balado in Kinross-shire last night.
He told fans: "Ladies and gentleman, I present to you - Scotland's own, Calvin Harris."
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Harris - a firm favourite with the festival crowd - opened by playing Under Control.
Revellers danced in the rain as he played for more than an hour, before Smith joined him back on stage for the final song shouting: "Scotland, I love you."
His headline set came after a performance from Paolo Nutini in which he saved Last Request until the end, much to the delight of the audience.
Festival-goers earlier covered up in waterproof ponchos as heavy downpours descended while Pharrell Williams took to the main stage.
The rain cleared-up during his 60-minute set, which he closed with hit single Happy.
The site near Kinross has been the festival's home since 1997 but this year's weekend-long event will be the last one to be held there before a move to the Strathallan Castle estate in Perthshire next year.
The Charlatans were welcomed back to the festival 18 years to the day they performed on the very first Saturday at Balado.
The Stranglers, Katy B and Scottish band Twin Atlantic, James and Rudimental were also included in the Saturday line-up.
Elsewhere, huge crowds cheered on local girl Nina Nesbitt in the King Tut's Tent and enjoyed a mass sing-along with James.
Organisers praised the the crowds for creating a "fantastic" atmosphere.
There was a total of 27 arrests by yesterday evening, with police saying the event caused officers "absolutely no concern at all".
Chief Superintendent Kevin Lynch said: "Everyone is well behaved and enjoying themselves.
"Crime levels are still low and the very small minority who do break the law are being dealt with appropriately."
Geoff Ellis, festival director, said: "We're delighted with the first day of the event and we're looking forward with mixed emotions to tomorrow for the very last day of T in the Park at Balado.
"We've got another incredible line-up, there's a fantastic atmosphere and it's going to be a day to remember."
Almost 500 people had been seen by the hospital tent, with Nick Moore, of the Scottish Ambulance Service, saying there was a "steady flow" of people at the first aid points.
The final day of T in the Park will see Arctic Monkeys become the last ever act to play the festival at its current home.
Paul Weller, Jake Bugg, Kaiser Chiefs, Bastille and Franz Ferdinand are also included in the line-up preparing to bid farewell to Balado.