New York, Sep 04: Former World No. 1 Novak Djokovic on Monday outclassed his Portuguese opponent Joao Sousa in straight sets to book his spot in the quarter-finals of the men's singles event in the ongoing US Open.

The Serbian ace maintained his 100 per cent win record against the Portuguese, having emerged victorious in the four previous clashes with Sousa without conceding a single set, with a 6-3, 6-4, 6-3 scoreline.

Serving first, Sousa, who entered the round-of-16 for the first time in his career, started the match positively and won the first game having held Djokovic to love. However, Djokovic won the successive game 40-0 and got the first break in the next.

A double fault from Sousa, with Djokovic having three set points and the score at 5-3, ensured the first set went the Serbian's way. The second set saw an improved showing from Sousa, who claimed his first break point in the third game after a double fault from Djokovic. The Serbian made amends in the next game and with the match level at 4 games each, the current World No. 6 won consecutive games to wrap up the second set.

Djokovic made light work of the Portuguese World No. 68 in the third set and won three back-to-back games with the scores level at 3-3 to cruise into the quarter-finals. The two-time US Open champion will be looking to win his second grand slam of the year after lifting the 2018 Wimbledon title.

Meanwhile, Japan's Kei Nishikori, Argentina's Juan Martín del Potro, and John Isner of the United States booked their spots in the quarter-final round of the men's singles event. Croatian Marin Cilic's clash against Belgium's David Goffin is underway. World No. 2 and five-time US Open champion Roger Federer is set to face John Millman of Australia on Tuesday for the last quarter-final berth.

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