Kozlov was the Spaniard’s training partner on Monday when he was called up at the last minute to replace the injured Frenchman Maxime Cressy in the main draw.
Barring a brief spell in the second set when he converted his only breakpoint chance in the match, Kozlov was no match for Nadal whose previous 11-0 best start in 2014 ended in a defeat to Swiss Stan Wawrinka in the final. Australian Open.
Next for the 35-year-old will be another 39th-placed American Tommy Paul with a potential semi-final clash against seeded Russian Daniil Medvedev, who he defeated in the Australian Open final with a two-set gap.
“It is always important to win as fast as possible, but the most important thing is to win,” said Nadal after his victory in one hour and 16 minutes in hot and humid conditions.
“Tonight there were two sets, this is excellent news and I will try to be ready for tomorrow again against a difficult opponent.”
Medvedev previously beat Pablo Andújar 6-1 6-2 and put himself three wins from winning the tournament and climbing to number one in the world rankings for the first time.
Medvedev pretended he could secretly serve at match point, but instead beat his seventh ace, causing a smile from the 68th-ranked Spaniard who played well but failed to break through the Russian’s solid defense.
Medvedev will soon face Japanese qualifier Yoshihito Nishioka and a title on Sunday for the Russian will ensure his climb to number one in the world rankings by replacing Serbian Novak Djokovic.
World number four Stefanos Tsitsipas also lost little time by eliminating American qualifier JJ Wolf, the French Open finalist who won 6-1 6-0 in just 47 minutes in the final game of the night on the main showcourt.
It was the 23-year-old Greek’s fastest completed victory in his career and next time he will meet 59th-ranked American Marcos Giron, who previously defeated Spaniard Pablo Carreño Busta 6-7 (7) 6-4 7- 6 (4), for a place in the semifinals.