It was a first-time victory in six attempts for the Bulgarian seventh seed against the Argentine former Grand Slam winner.
Grigor Dimitrov beat Juan Martin del Potro 6-3 7-5 to book a place in the quarter-final of the Cincinnati Open in Ohio, USA
The Bulgarian next face Japan’s Yuichi Sugita who came from a set down to beat Karen Khachanov of Russia 6-7, 6-3, 6-3.
Third seed Dominic Thiem also marched on with a hard fought 7-6 7-6 victory over Frenchman Adrian Mannarino while John Isner beat fellow American world number Frances Tiafoe 7-5, 7-6.
In an all Spanish affair, David Ferrer beat Carreno Busta 6-4 6-4 to also advance through to the quarters.
Thiem and Ferrer will meet in the quarter-final.
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