HARRY Potter and the Half-Blood Prince, the sixth instalment in the boy wizard series, has debuted at the top of the North American box office. The movie has raked in $159.6m (96.7m) since it opened on Wednesday, according to early estimates. The Half-Blood Prince beat the opening figures for The Order of the Phoenix, which was released in 2007 and took $139.7m (84.6m) in its opening week. Ice Age: Dawn of the Dinosaurs held steady at number two. The third film in the animated series took $17.7m (10.7m) over the weekend. The Transformers sequel, Revenge of the Fallen, is at number three. Sacha Baron Cohens latest film, Bruno, dropped into fourth place following its debut at number one last week, with takings of $8.4m (5m) over the weekend. The mock documentary made over $30m (18m) in its first week. Romantic comedy 500 Days of Summer - starring Zooey Deschanel and Joseph Gordon-Levitt - entered the chart at number 12, despite a limited release in just 27 cinemas. - BBC