Alexander Zverev won the season-ending ATP Finals in 20182020 Australian OpenVenue: Melbourne Park Dates: 20 January to 2 FebruaryCoverage: Listen on BBC Radio 5 Live Sports Extra and online; Live text on selected matches on the BBC Sport website and app; Watch highlights on BBC Two and BBC iPlayer.Alexander Zverev is through to a Grand Slam semi-final for the first time after defeating Stan Wawrinka in four sets at the Australian Open. The German seventh seed beat the Swiss three-time Grand Slam champion 1-6 6-3 6-4 6-2, dropping a set for the first time in Melbourne this year.He lost the first five games in only 16 minutes but bounced back to convert five out of 13 break points.The 22-year-old will face Rafael Nadal or Dominic Thiem in the last four.World number one Nadal takes on Austrian fifth seed Thiem on the Rod Laver Arena at 08:30 GMT on Wednesday. Wawrinka, who won the Australian Open in 2014, has now been knocked out at the quarter-final stage in three of the past four Grand Slams.The 34-year-old started strongly against Zverev, racing through the opening set and winning 16 out of 19 points on his serve, even though his first-serve percentage was only 32%.But Zverev really stepped up in the second, not dropping a point in five service games and breaking once to level at one set all.Both players lost their opening service games at the start of the third, before Zverev moved 4-2 up and then served out the set.The German opened up a 4-0 lead in the fourth as Wawrinka sprayed shots all over the court, possibly feeling the effects of two five-set matches earlier in the tournament against Andreas Seppi and Daniil Medvedev.Zverev, who had not gone beyond the fourth round in Melbourne prior to this year, said: “I don’t know what to say. I’ve done well in other tournaments, I’ve won Masters, I’ve won the ATP Finals, but I never could break that barrier in a Grand Slam. I’m happy to be in the semi-finals.” Addressing the crowd, he added: “You guys cannot imagine what this means to me and I hope it will be the first of many.”In the other semi-final, 20-time Grand Slam champion Roger Federer will face last year’s Australian Open winner Novak Djokovic on Thursday.