Germany’s Angelique Kerber has stunned world number one Serena Williams in three sets to win her first Grand Slam title at the Australian Open.The 28-year-old is the first German to win a major singles title since Steffi Graf at the 1999 French Open.Williams, 34, was beaten for just the fifth time in 26 Grand Slam finals, and the American missed the chance to tie Graf’s open-era record of 22 titles.