NEW YORK: Teenager Bianca Andreescu became Canada’s first Grand Slam singles champion on Saturday with a rollercoaster 6-3, 7-5 win over 23-time major champion Serena Williams in the US Open final.The 19-year-old Andreescu became the youngest Grand Slam winner since Svetlana Kuznetsova at the 2004 US Open, handing Williams a fourth consecutive defeat in the final of a major to again deny her a record-equaling 24th Slam title.