By Caroline Briggs
BBC News entertainment reporter, O2 Arena
Madonna: "Long live the King"
Madonna kicked-off her revamped Sticky And Sweet tour at London's O2 Arena with a tribute to Michael Jackson.
Jackson, who died last week, was due to perform a series of 50 farewell concerts at the venue from 13 July.
As Madonna sang Holiday she was joined by a dancer dressed in Jackson's unmistakable style of sequined jacket and sparkling white glove.
Madonna told the crowd: "Give it up for one of the greatest artists the world has ever known - long live the King!"
Pictures of Jackson as a boy flashed up on a giant screen as the dancer moon-walked across the stage to the strains of Billie Jean.
He went on to perform some of Jackson's signature moves to Wanna Be Starting Something.
An estimated crowd of 17,000 watched Madonna perform at the first of two concerts in London this weekend.
She moves on to Manchester on Tuesday, followed by several dates across Europe.
Madonna closed the show with Give It 2 Me, and donned a jewelled glove, along with her dancers, in a final, simple, tribute to Jackson.
Lyrics from his hit Man In the Mirror scrolled across the screens. It read: "If you want to make the world a better place, take a look at yourself and then make the change."
Jackson and Madonna both became huge solo stars in the 1980s
The tribute, albeit brief, impressed fans at the O2. Victoria Mears, of Billericay, Essex, said: "I really liked it. It seemed very fitting for the queen of pop to pay tribute to the king of pop."
Nina Lawrence, 32, of Bishop's Stortford, Hertfordshire, said: "I thought it was good, but it was a shame she didn't sing one of his songs as a tribute."
And Helen Levy, 30, of Winchester, Hants, said: "She seemed very passionate when she spoke about Michael Jackson. It's clear that he was a great inspiration to her."
Jackson and Madonna both became huge solo stars in the 1980s.
Speaking after the 50-year-old's death on 25 June, Madonna said: "I can't stop crying over the sad news.
"I've always admired Michael Jackson - the world has lost one of its greats, but his music will live on forever."
A public memorial service for Jackson will be held at the Staples Center in Los Angeles on Tuesday.
More than 1.6m fans applied for just 17,500 tickets available for the event.