The top two seeds were upset in the doubles draw on Tuesday at the Belgrade Open in Serbia.
Federico Delbonis and Artem Sitak ousted top seeds Rohan Bopanna and Franko Skugor 6-3, 4-6, 10-8 to reach the quarter-finals. This is their second team appearance after making the second round at the Great Ocean Road Open earlier this year.
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The unseeded duo will next play Serbia Open champions Ivan Sabanov and Matej Sabanov. The winning team will challenge Jonathan Erlich and Andrei Vasilevski, who defeated Sander Arends and Luis David Martinez 6-3, 0-6, 10-6 in the last eight.
Americans Austin Krajicek and Tennys Sandgren made the quarter-finals with a 6-3, 6-7(5), 10-8 victory against second seeds Fabrice Martin and Hugo Nys. Other teams that moved on Tuesday were fourth seeds Marcelo Demoliner and Santiago Gonzalez as well as Luke Bambridge and Dominic Inglot.