Nole goes on to play Feliciano Lopez (ESP, H2H 8-1) in the last 16 on Thursday.
Next up for the two-time former champion is no.13 seed Pablo Carreno Busta (ESP).
Novak and Viktor saved one match point en-route to a 5-7, 6-1, 11-9 victory over Pierre-Hugues Herbert and Nicolas Mahut. They face Klaase/Ram in quarter-finals.
Novak advanced past the Argentine 4-6, 6-4, 6-4 in two hours and 38 minutes to move to 12-4 in their ATP Head2Head series.
The reigning Paris Masters champion beat world no.34 Gilles Muller 6-3, 6-4 and next faces no.14 seed Grigor Dimitrov (Thursday).