Dennis has played mostly Futures and Challengers, reaching the quarter-, semi-, and finals of a number of events, but never winning a title. He qualified for the 2012 SAP Open in San Jose, California. He lost his first main-draw match to Bulgarian Dimitar Kutrovsky, another qualifier.
In the first match of the day, American Dennis Lajola lost his ATP Tour debut to fellow qualifier Dimitar Kutrovsky of Bulgaria, 6-7 (7), 6-3, 7-6 (3)
GO Roger Federer, Nick Kyrgios, Borna Coric, Vasek Pospisil, Kei Nishikori, , Milos Raonic, Jerzy Janowicz, Grigor Dimitrov, Dennis Novikov and Bernard Tomic and Mikael Ymer
Thiem will be No 1 by Dec 2017
Nick Kyrgios will be No 1 by Sep 2018
Mikael Ymer will be No 3 by Dec 2018
Alexander Zverev will be No 3 by Dec 2017