German star Alexander Zverev could only raise his thumb in salute after his Australian Open semi-final opponent Dominic Thiem delivered an act of perfect sportsmanship on Friday night.
In a tense third set where the match remained up in the air, Thiem forfeited a point that ended up costing him dearly as the two close friends fought for a chance to face Novak Djokovic in Sunday's final.
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In a tight deuce game, Zverev struck a loopy groundstroke that appeared to land beyond the baseline before Thiem half-heartedly returned the ball over the net as the linesman called Zverev's ball out.
Zverev turned to face Thiem immediately after the point only for Thiem to take a close inspection of the mark on the surface and gesture to his rival to challenge the linesman's ruling. According to Channel 9 commentators, he even yelled out across the net for Zverev to send the decision to Hawkeye.