Roger Federer has had many improbable victories in his career, and a smattering of unusual defeats, but his passage into the semi-finals of the 2020 Australian Open after three-and-half hours of undiluted drama against Tennys Sandgren was in another dimension. He won 6-3, 2-6, 2-6, 7-6 (8), 6-3 to put the world No 100 away on a warm, sticky afternoon on Rod Laver Arena and set up a semi-final against Novak Djokovic, who later saw off Milos Raonic – but those are the bare bones of the story. On his way to his second great escape of the week, the six-times winner of this title and owner of a record 20 majors had to save seven match points, received a rare code violation for swearing, snarled at one of the game’s best chair umpires, Marijana Veljovic, then made the most of his luck when Sandgren was within sight of victory and injured his right knee in a collision with a ball girl. “Got to get lucky some times, I tell you that,” Federer said courtside. “Those seven match points I wasn’t under control. I was hoping he was not going to smash the winner. He played his match. I got…