In the final of the US Open Tennis Tournament Men’s Singles event in 2015, Novak Djokovic defeated Roger Federer.
Option 1: Tommy Robredo - This option is incorrect as Tommy Robredo was not defeated by Novak Djokovic in the final of the US Open in 2015.
Option 2: Fabio Fognini - This option is incorrect as Fabio Fognini was not defeated by Novak Djokovic in the final of the US Open in 2015.
Option 3: Roger Federer - This is the correct option. Novak Djokovic defeated Roger Federer in the final of the US Open in 2015.
Option 4: Pablo Cuevas - This option is incorrect as Pablo Cuevas was not defeated by Novak Djokovic in the final of the US Open in 2015.
Therefore, the correct answer is Option 3: Roger Federer.