Germany's Alexander Zverev remained on track for a return to the Australian Open final after beating American Learner Tien 6-3 6-7(5) 6-1 7-6(3) in the Melbourne Park quarterfinals on Tuesday.
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The big-serving third seed, who finished runner-up to Jannik Sinner last year, will face either Carlos Alcaraz or Alex de Minaur in the last four in what will be his fourth semifinal at the event.
Zverev secured a break in the sixth game of the opening set when 20-year-old Tien sent a crosscourt backhand just beyond the tramlines to give the German the upper hand.
There was little between the pair in the second set, which Tien shaded in the tiebreak having beaten Zverev with a fine passing shot to set himself up for a set point that he gleefully converted.
However, Zverev pulled clear in the third set, eliminating the unforced errors and breaking twice to ease ahead.
The fourth set went on serve but Zverev took command in the tiebreak and booked his place in the next round.