Moments after Djokovic clinched victory, Safiullin served out to win a final-set tie-break against American 13th seed Frances Tiafoe.

Tiafoe, 26, reacted angrily towards chair umpire Jimmy Pinoargote after losing 5-7 7-5 7-6 (7-5), launching a flurry of expletives in the Ecuadorian official's direction.

Tiafoe could face a fine of up to $60,000 (46,000) for the outburst, classified as a verbal abuse offence in the ATP rules.

The incident could be escalated if tournament officials feel it was 'flagrant and particularly injurious to the success of a tournament, or singularly egregious'.

If Tiafoe's actions are considered an 'offence of aggravated behaviour' or 'conduct contrary to the integrity of the game', the two-time US Open semi-finalist could face a larger fine.

Tiafoe's outburst came after a defeat that turned on the American being given a time violation at 5-5 in the tie-break.

He claimed he tossed the ball up to serve, but Pinoargote disagreed it was a legitimate throw intended to start the point and penalised him.

Forced to start with a second serve, Tiafoe lost the point after an exciting all-court exchange for 6-5 to Safiullin, who clinched victory at the first attempt.

Meanwhile, American seventh seed Taylor Fritz, Bulgarian ninth seed Grigor Dimitrov and Greek 10th seed Stefanos Tsitsipas were among the other winners on Tuesday.

Tsitsipas beat France's Alexandre Muller to set up a fourth-round meeting with Russian fifth seed Daniil Medvedev, relaunching a rivalry that has provided drama in the past.