Damon Albarn and Graham Coxon staged a mini-Blur revival as rain fell on the Latitude festival.
Guitarist Coxon joined his former bandmate on stage for an encore as thunder rumbled and lightning forked across the sky above the main arena at Henham Park in Suffolk.
After a solo rendition of early song End Of A Century, Damon told the crowd: "There are some Blur songs I can play on the piano, but this one would be impossible without the man I wrote it with."
Graham took to the stage and the pair played hit single Tender to a delighted but drenched crowd.
Graham left the band suddenly in 2002. Since then his friendship with Damon was said to be troubled. But the band reformed for a string of appearances in 2009 after saying they had rebuilt their relationship.
They promised to revive the act occasionally in future. After performing a largely solo set, Damon also embraced his more recent past with a performance with his Gorillaz collaborators. Following soaring temperatures on the first day of the festival, today was cooler with occasional rain.
Campers face the prospect of a wet and muddy final day - headlined by the Black Keys - with more downfalls predicted overnight.
Lily Allen earlier tackled her critics head-on at the festival, headlining the packed main arena on the opening night.
The singer took the place of Two Door Cinema Club after they pulled out at the last minute due to illness. Earlier in the day, Allen said she was "exhausted by nastiness" on Twitter 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.
Towards the end of her performance, she said: "I wish I could stay longer but I'm supposed to be on holiday. I'm off to Spain in the morning and my babies are asleep in a tour bus right now."
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 her father Keith, she said: "I'm really excited to be here."
Wearing a multi-coloured kaftan over ripped denim shorts and a white vest top with silver trainers, she left the stage in a gondola after performing the song As Long As I Got You.
Other highlights included Bombay Bicycle Club, Royksopp and Robyn and comedian Simon Amstell.