U.S. pop star Madonna kept her sexy image alive by wearing over-the-knee leather boots during the start of her world tour in Wales, her representative says.

The unidentified representative told People magazine the "Material Girl" star had been working until the last minute to ensure Saturday night's performance at Millennium Stadium in Cardiff, Wales, would be a success.

"She's been putting the finishing touches to some of the dance routines today, in a good way, she's a perfectionist," the representative said.

The 50-year-old also got some on-screen help to begin her Sticky and Sweet tour from Justin Timberlake, Britney Spears and Kanye West. The three singers joined her for "4 Minutes."

The entertainer also took time during the performance to speak with her 40,000 assembled fans through a video message containing images of war, poverty and top proponents for positive change in the world, People said.