Defending champion Alexander Zverev moved a step closer to reaching the final of the BMW Open on Wednesday, as rising star Frances Tiafoe ousted Gilles Muller in Estoril.
Zverev wasted two set points in a lengthy first-set tie-break before overcoming Yannick Hanfmann 6-7 (12-14) 6-4 6-2.
Up next for the holder at the ATP 250 event in Munich will be another German opponent, Jan-Lennard Struff having beaten Yannick Maden in three sets.
Hyeon Chung, the fourth seed, is on course to meet Zverev in the semi-finals, should the impressive young Korean get the better of Martin Klizan.
Chung brushed aside Matthias Bachinger 6-1 6-1, while Klizan, Novak Djokovic's recent conqueror in Barcelona, had to come from a set down to beat Mirza Basic.
American Tiafoe defeated world number 28 Muller, the fourth seed and last year's beaten finalist, 6-4 7-5 at the Estoril Open.
Joao Sousa won an all-Portuguese showdown with Pedro Sousa 4-6 7-6 (7-1) 7-5, while third seed Kyle Edmund saw off young Australian wildcard Alex de Minaur and Simone Bolelli edged out Federico Delbonis.
Laslo Djere sprung one of several surprises at the Istanbul Open, beating third seed Andreas Seppi 6-3 6-7 (4-7) 6-3.
Rogerio Dutra Silva and Taro Daniel also defeated higher-ranked opponents, accounting for sixth seed Viktor Troicki and fourth seed Aljaz Bedene respectively.
Marco Trungelliti could not follow suit, though, fifth seed Paolo Lorenzi winning their match 6-2 7-6 (7-5).
