World number one Novak Djokovic held firm to progress past a resilient Roberto Bautista Agut and book a place in the quarter-finals of the US Open this evening, securing a 6-3 4-6 6-4 6-3 victory at Flushing Meadows.

Djokovic started the contest in a typically intense fashion as he battled to within four break points of taking an early lead over Agut come game four, but he was initially unable to make the pressure count as the Spaniard battled back to hold at the vital moment.

Agut then produced some impressive tennis of his own in game six, where he was able to push Djokovic close to surrendering his serve, only for the Serbian star to come off with a memorable ace and a strong first service to clinch a hold of his own.

Djokovic moved on in a dominant fashion after that wake-up call, and he took a vital break in the eighth to secure control of the first set, which he eventually took 6-3 following a standout forehand smash winner.

The world number one's intensity continued to grow and it soon proved too much for Agut first up in the second set, as Djokovic broke his opponent as early as the third game.

It appeared as though Djokovic would press on for a quick victory, but Agut planted a major seed of doubt having broken the Serbian's serve to make it 4-4 at the midway point of the second offering, as his forehand looked to be causing all kinds of problems.

The break looked to have boosted the confidence of Agut, and he did not seem to look back as he went on to break Djokovic again to take the second set 6-4 and apply some real pressure on the Serbian's return game.

Looking to respond to losing his first set at this year's Open, Djokovic battled back to break his opponent in the fifth game of the third, with Agut clearly tiring following his impressive efforts earlier in the contest.

That break proved vital for Djokovic as he marched on to hold throughout the third set and eventually seal it 6-4, having held off on his own service to move in front with victory in the 10th game.

Agut appeared spent at the start of the fourth set and he gifted Djokovic an easy break in the first game, as he found it hard to land much of his return work within the court.

With his conditioning evidently worse than his Serbian counterpart's, the Spaniard made one last effort with more impressive forehand work to break back against Djokovic, who did not help himself by supplying his opponent with easy return winners at 2-2.

The break only appeared to inspire Djokovic, however, as he produced a memorable drop shot over the net to break straight back and take a 3-2 advantage, which he rarely failed to ponder on after moving to close out a 6-3 victory in the decisive set.