On Wednesday, Djokovic beat Yoshihito Nishioka 6-1, 6-2 to clinch the win after Filip Krajinovic beat Yuichi Sugita 6-2, 6-4. The Serbian wrapped up the contest in just one hour and seven minutes when one last potent first serve forced a return error.
In doubles, Viktor Troicki/Janko Tipsarevic gave Serbia the 3-0 win with a 7-6(5), 7-6(4) victory against Yasutaka Uchiyama/Ben McLachlan.
Japan, meanwhile, has been eliminated from tennis's premier international team competition following losses in both of their round-robin matches in Group A.
Three-time Grand Slam singles champion Andy Murray, playing in his first Davis Cup match since 2016, came back from 1/4 down in the deciding-set tie-break to help Great Britain beat the Netherlands 2-1. Murray defeated Tallon Griekspoor 6-7(7), 6-4, 7-6(5).
Dutchman Robin Haase beat Daniel Evans 3-6, 7-6(5), 6-4 and in doubles, Neal Skupski/Jamie Murray gave Great Britain the victory with a 6-4, 7-6(6) win against Wesley Koolhof/Jean-Julien Rojer.
Spain booked their place in the quarter-finals as Roberto Bautista Agut and World No. 1 Rafael Nadal didn't drop a set against Croatia. Bautista Agut dismissed Nikola Mektic 6-1, 6-3 and Nadal beat Borna Gojo 6-4, 6-3.
Germany's Jan-Lennard Struff beat Argentina's Diego Schwartzman 6-3, 7-6(8) to help the Germans earn the 3-0 sweep. Struff hit 12 aces and won 80 per cent of his first-serve points.
Philipp Kohlschreiber also won, beating Guido Pella 1-6, 6-3, 6-4 and in doubles ATP Finals qualifiers Kevin Krawietz/Andreas Mies beat Leonardo Mayer/Maximo Gonzalez 6-7(4), 7-6(2), 7-6(18).
( With inputs from IANS )