Defending champion Rafael Nadal's progress into the US Open quarter-finals was far from smooth as he needed four sets to beat unseeded Georgian Nikoloz Basilashvili. The 32-year-old Spaniard led by two sets to love before Basilashvili, ranked 37th in the world, recovered to take a third-set tie-break. But the top seed broke twice as Basilashvili faded physically in the fourth to win 6-3 6-3 6-7 (6-8) 6-4. He faces ninth seed Dominic Thiem next. Nadal has reached at least the quarter-finals in all four Grand Slams this year – the first time he has achieved the feat since 2011. Austria's Thiem knocked out South African fifth seed Kevin Anderson – the man who lost in the final to Nadal at Flushing Meadows last year – in three sets earlier on Sunday. For Thiem, Tuesday's quarter-final offers a chance to avenge a defeat by Nadal in his first Grand Slam final at June's French Open. Nadal had to dig deep to beat powerful Russian Karen Khachanov in the third round, fighting back from a set and a break down – also overcoming a slight knee injury – to win one of the most thrilling matches of this year's tournament so far. Two days later Nadal, who played without any strapping on his right knee, needed another three hours 19 minutes to overcome Basilashvili. "I've had tough matches in a row," said Nadal, who is chasing an 18th Grand Slam title. "This was a physical one but I feel good." After needing four hours and 23 minutes to beat Khachanov, it means Nadal has spent more than seven-and-a-half hours on court in three days and could face a physical encounter against another heavy hitter in Thiem. "It'll be a tough one against Thiem. He hits the ball strong and has a big serve," Nadal added. The problems Nadal faced came virtually out of nowhere. The three-time US Open champion cruised into a two-set lead in little over an hour – ominous signs for Basilashvili, who had won one game against Nadal in their only previous meeting at the 2017 French Open. This time, the 26-year-old Georgian coped much better with the intensity of facing one of the world's greats. Basilashvili's approach was all or nothing against the world number one, although unforced errors outstripped winners in the opening two sets before he began to find his range in the third. Twenty-three winners from his racquet forced Nadal to face some uncomfortable moments. Despite fatigue appearing to kick in before the breaker, Basilashvili found some energy reserves to outfight his illustrious opponent and take the match further. "He was hitting the ball very strong, it felt like I wasn't controlling the points," Nadal said. However, Basilashvili could not maintain this level in the fourth set as Nadal broke for a 4-3 lead which he would not relinquish. (BBC Sport)