The Australian looked disinterested throughout his match with Cameron Norrie.
The American has five Olympic medals, tied for the tennis lead.
Diego Schwartzman was also added on Friday.
The Austrian fell in a pair of tiebreaks, as defending champion Leo Mayer rolled along.
Frances Tiafoe and Jeremy Chardy each lost.
Nikoloz Basilashvili and Nicolas Jarry also reached the final eight.
Both have won the hard court event in their careers.
The 36-year-old cited the need to lighten his schedule.
The 25-year-old defeated Guido Pella in straight sets on Sunday evening.
The Latvian grabs her first championship of the season.
Johnson goes for his second win of the season; Ramanathan makes his first career final.
The Italian goes for his second career title, the Argentine his first.
Petra Martic and Polona Hercog complete the semifinal lineup.
Guido Pella and Marco Trungelliti complete the semifinal lineup.
Marcel Granollers knocked off top seed Adrian Mannarino on Friday.
They'll meet in an anticipated Saturday semifinal.
No. 6 seed Robin Haase also reached the quarterfinals.
Amid driving rain, Cirstea finished her victory at close to one-o'clock in the morning.
It's a first ever tour-level semifinal for each player.
Top seed Alize Cornet joined them in the final eight in Switzerland.