Nick Kyrgios is playing some of the best tennis of his life in 2017.Some love him, and some hate him, but no one can avoid him when he's playing this well. The Australian reached the semi-finals of the Miami Open on Thursday evening, beating Alexander Zverev 6-4, 6-7, 6-3 in a tough match. He will play Roger Federer on Saturday, looking to book a place in the final against either Rafa Nadal or Fabio Fognini, who complete the last four.Federer, who won the Australian Open in January, will be tough competition for the 21-year-old.However, Kyrgios will be quietly confident ahead of the matchup after coming through a crunch match against Zverev yesterday.  It wasn't the cleanest of victories, and as usual, the Kyrgios win came with controversy.Tempers flared on court as chair umpire Fergus Murphy made a contentious decision in the deciding set.Zverev mishit a lob shot, and the ball sailed long past the line but was mistakenly called in by the linesman. The Australian returned, mishitting a shot of his own, before challenging the decision.Umpire Murphy allowed the challenge and after replay's confirmed the German's original shot was out, Kyrgios won the point.    Zverev, who was understandably upset with the call, argued to the umpire that his opponent shouldn't have been allowed to challenge the call after hitting the ball back.Despite his protests, the call stood, and Kyrgios went on to win the match.Although the umpire's mistake may have taken the shine of the Australian's victory, there was plenty to admire from Kyrgios's display.In the first game of the second set, the number 12 seed pulled off a 'tweener' shot, returning Zverev's shot with his racket between his legs.Commentator's described it as "something out of the ordinary", but it's a shot we're beginning to get used to seeing from the Australian.At 30-love down in the game, many players would get flustered at the idea of losing another point, but Kyrgios kept his cool and placed his shot perfectly across court. A video of his latest 'tweener' can be seen below.

With both Federer and Nadal in the semi's of the Miami Open, Kyrgios has his work cut out to reach the final. He was knocked out by Kei Nishikori at the same stage last year.   

Fognini, who is currently ranked 40th in the world, would also love to create a huge upset by beating Nadal in his match, but a repeat of the Australian Open final looks likely.