The Serbian, who has dominated the ATP Tour this year, including winning three of the four Grand Slams, and will end the year as the world number one for a record seventh time, dispatched his Norway opponent with relative ease. 

Ruud put up a fight in the first set, eventually falling short in the tiebreak, before Djokovic ran out a comfortable victor in the second set, winning 7-6, 6-4.

Djokovic's 90 per cent points won on his first serve was telling, while Ruud created just one breakpoint opportunity, which he failed to convert, and committed four double faults.

In the other Green Group match of the day, Russia's Andrey Rublev bettered Greece's Stefanos Tsitsipas 6-4, 6-4.

Rublev also won 90 per cent of his first-serve points and did not face a single breakpoint. 

Conversely, he created seven breakpoint opportunities, despite only winning two of them, and won 39 per cent of his return points, proving how dangerous he was in Tsitsipas' service games.

Play continues tomorrow with Russia's defending champion Daniil Medvedev against Germany's Alexander Zverev and Hubert Hurkacz of Poland against one of two Italians, Matteo Berrettini, who had to retire early against Zverev in his opening match, or Jannik Sinner, who is waiting on standby.