In their first match together, the US-German pairing prevailed 6-1, 3-6, 10-7 to set a last-eight showdown with second seeds Jamie Murray and Bruno Soares or Marcelo Arevalo and Federico Delbonis. Mies – a two-time Roland Garros doubles champion alongside Kevin Krawietz – underwent knee surgery earlier this year and only returned to action in Toronto.
The duo won 68 per cent of first-serve points and 32 per cent on second serves. They broke the British-Italian tandem four times.
Brandon Nakashima and Sem Verbeek made good on their main draw doubles wild card, rebounding to defeat Grigor Dimitrov and Jean-Julien Rojer 4-6, 6-3, 10-7. The US-Dutch duo will meet top seed Joe Salisbury and Neal Skupski for a place in the semi-finals.
At the Sofia Open, third seeds Oliver Marach and Philipp Oswald reached the quarter-finals with a narrow victory over Rohan Bopanna and Aisam Ul-Haq Qureshi. The Austrians notched a 6-2, 6-7(1), 10-7 win to set a clash with Brazilians Marcelo Demoliner and Rafael Matos.
Roman Jebacy and Matwe Middelkoop booked their quarter-final berth at the expense of Bulgarian wild cards Adrian Andreev and Alexandar Lazarov. The Czech-Dutch pair advanced 6-2, 6-4 in just under an hour. They await top seeds Henri Kontinen and Ben McLachlan or Jonathan Erlich and Dominic Inglot.