Shanghai Masters: Novak Djokovic overtakes Flavio Cobolli in ATP event

Shortly after Djokovic clinched the win, Safiullin served to win a final set tiebreaker against 13th-seeded American Frances Tiafoe.

The 26-year-old Tiafoe reacted angrily to referee Jimmy Pinoargote after losing 5-7, 7-5, 7-6 (7-5) and unleashed a barrage of expletives towards the Ecuadorian referee.

Tiafoe could face a fine of up to $60,000 (£46,000) for the outburst, which is classed as a verbal abuse offense under ATP rules.

The incident could escalate if tournament officials believe it is “flagrant and particularly detrimental to the success of a tournament or particularly egregious.”

If Tiafoe's actions are deemed an “offense of serious conduct” or “conduct contrary to the integrity of the game,” the two-time US Open semifinalist could lose his prize money.

Tiafoe's outburst came after a loss in which the American received a time violation with the score tied at 5-5 in the tie-break.

He claimed he threw the ball up to serve, but Pinoargote disagreed that it was a legitimate throw meant to open the point and penalized him.

Tiafoe had to start with a second serve and, after a thrilling all-court exchange, lost the point 6-5 to Safiullin, who secured victory on the first attempt.

Other winners on Tuesday included seventh-seeded American Taylor Fritz, ninth-seeded Bulgarian Grigor Dimitrov and 10th-seeded Greek Stefanos Tsitsipas.

Tsitsipas defeated Frenchman Alexandre Muller and met fifth-seeded Russian Daniil Medvedev in the fourth round. In doing so, he reignited a rivalry that had caused drama in the past.