MELBOURNE, Jan 21 (Reuters) - Sixth seed Rafa Nadal dropped his first set at this year"s Australian Open but still powered through to the fourth round with a 6-3 6-2 3-6 6-1 defeat of Karen Khachanov on Friday. The Spaniard, seeking to claim a record 21st Grand Slam title in the absence of great rivals Roger Federer and Novak Djokovic, was sensational as he took a two-set lead. But Khachanov, seeded 28th, threw caution to the wind in the third set, stalling Nadal"s charge with some ferocious hitting. Olympic runner-up Khachanov had lost all seven previous meetings with 2009 Australian Open champion Nadal but briefly looked capable of mounting a comeback. Nadal seized back control with a break of serve at the start of the fourth, however, and with the clock having ticked past midnight on Rod Laver Arena he finished it off in a hurry. Nadal, who has reached the last-16 in Melbourne for the 15th time in 17 appearances, will face another Russian, 18th seed Aslan Karatsev, or Frenchman Adrian Mannarino next. "I played a great player tonight and happy that this was my best match since coming back," the 35-year-old Nadal, who missed the second half of 2021 with a foot injury, said on court. "I"ve been going through some tough times in the last year but night"s like tonight mean everything." With Federer still injured and nine-time Australian Open champion Djokovic deported after a visa row, Nadal has a chance to edge ahead of that duo with whom he shares the record for most men"s Grand Slam titles. After routine wins against 66th-ranked American Marcos Giron and German qualifier Yannick Hanfmann in rounds one and two, Khachanov represented a step up in class for Nadal despite the Russian having only ever won one set off the Mallorcan. Nadal was primed though and won 12 of the first 13 points to stamp his authority all over the court. Khachanov had no answer to Nadal"s intensity and managed to win only one point on Nadal"s serve in the opening set. Nadal broke serve at the start of the second set but Khachanov won an incredible point in the fourth game, picking himself off the floor to crunch a backhand winner and then winning another incredible rally to earn a break point. He could not convert that and Nadal immediately broke in the next game on his way to a two-set lead. Khachanov began to hit closer to the lines and with more menace in the third set, which he took after breaking the Nadal"s serve for the first time for a 3-1 lead. Nadal simply found another gear though, firing a stunning backhand winner to break Khachanov"s serve, and spirit, in the second game of the fourth set.