Germany's Angelique Kerber celebrates beating Madison Keys of the US in their women's singles quarter-finals match on day 10 of the Australian Open tennis tournament in Melbourne on January 24, 2018. Pic/ AFP 

Former champion Angelique Kerber signalled her intent to wrest back the Australian Open title as she brutally crushed US Open finalist Madison Keys on Wednesday to reach the semi-finals. The 2016 winner, seeded 21, brushed aside the American 17th seed 6-1, 6-2, breaking her much-vaunted serve at will as she triumphed in 51 one-sided minutes on Rod Laver Arena.