The Serbian hit 14 aces and broke Struff three times to advance in 76 minutes. The World No. 1 will continue his quest for a first Olympic singles gold medal against Alejandro Davidovich Fokina after the Spaniard beat Australian John Millman 6-4, 6-7(4), 6-3.
Having claimed the first three major championships of the year, drawing level with Roger Federer and Rafael Nadal on 20 Grand Slams after his Wimbledon triumph, Djokovic is aiming to become the first man to win all four majors and a gold medal in a season. WTA legend Stefanie Graf completed this achievement in 1988.
Second seed Daniil Medvedev, who is making his Olympics debut, produced a dominant display to overcome Indian Sumit Nagal 6-2, 6-1. The ROC’s Medvedev did not face a break point on his way to victory in 67 minutes.
Germany’s Alexander Zverev also moved through safely with a 6-2, 6-2 triumph over Egyptian Daniel Elahi Galan in 71 minutes. The World No. 5 won 87 per cent (26/30) of his first-service points and will next face Nikolaz Basilashvili after the Georgian moved past Italian Lorenzo Sonego 6-4, 3-6, 6-4.
Spaniard Pablo Carreno Busta battled back to beat Marin Cilic 5-7, 6-4, 6-4 in two hours and 25 minutes. The sixth seed next plays Dominik Koepfer after the German beat Australian Max Purcell 6-3, 6-0.