In October 2006, Girls Aloud released their first greatest hits collection, "". It debuted at number one on the UK album chart and went on to sell over one million copies. The album was accompanied by the single "Something Kinda Ooooh". Girls Aloud became the first British act to reach the top five purely on download sales; the single peaked at number three following its physical release. The next single was a cover of "I Think We're Alone Now" which peaked at number four on the UK Singles Chart. In March 2007, Girls Aloud collaborated with fellow British girl group Sugababes for the cover of the song "Walk This Way" by Aerosmith. Billed as "Sugababes vs. Girls Aloud", the song served as the official single for "Comic Relief" which became the group's third number one. In May 2007, Girls Aloud embarked on their third tour, The Greatest Hits Tour.