Rafael Nadal achieved his best start to an ATP Tour season on Tuesday, improving to 12-0 this year by defeating Stefan Kozlov to reach the Mexican Open quarter-finals.

The 35-year-old Spanish left-hander eliminated the US lucky loser 6-0, 6-3, advancing to a Thursday matchup against 39th-ranked American Tommy Paul, whom he has never played before.

"Always it's important to win as quick as possible, but the most important thing is to win," Nadal said. "Tonight has been straight sets. That's great news and I'll try to be ready for tomorrow again against a tough opponent."

The victory kept Nadal unbeaten over a dozen matches in 2022, his best career start to any year, surpassing the 11-0 run in 2014 that ended with a loss to Swiss Stan Wawrinka in the Australian Open final.

Nadal won his men's record 21st Grand Slam title at last month's Australian Open, breaking the career mark of 20 Slam crowns he had shared with Novak Djokovic and Roger Federer.

World number five Nadal, seeking his 91st career ATP title and fourth Acapulco crown, also won a warm-up tournament last month in Melbourne.

Nadal broke for a 2-0 lead when Kozlov netted a backhand and broke again on forehand smashes in the fourth and sixth games to sweep the opening set in 32 minutes.

Another forehand smash to break put Nadal ahead 3-1 in the second set but Kozlov broke back within 4-3 when Nadal netted a backhand volley.

Kozlov handed back the break in the next game on a botched backhand and Nadal held serve once more to advance after 76 minutes.

Spain's Rafael Nadal defeated American Stefan Kozlov on Wednesday to advance at the ATP Mexico Open
Spain's Rafael Nadal defeated American Stefan Kozlov on Wednesday to advance at the ATP Mexico Open AFP / PEDRO PARDO

"A little bit of a strange match," Nadal said. "Kozlov has a different style than most other players, so you need to be very careful.

"Sometimes you are able to win points in a row, but then if you start to play at his rhythm, it's very difficult because he has great control from the baseline and he's very smart."

Reigning US Open champion Daniil Medvedev, whom Nadal rallied past in five sets in the Australian Open final, beat Spain's 68th-ranked Pablo Andujar 6-1, 6-2 to continue his quest for the world number one ranking.

"It's pretty tough conditions, quite humid. Even if we play at night it's quite hot," second-ranked Medvedev said. "The faster the matches, the better you're going to feel for the next one."

Medvedev and Nadal could meet in a Friday semi-final.

If Medvedev wins the Acapulco title, he will overtake Djokovic atop the rankings no matter how the Serbian star fares this week at Dubai.

Medvedev would become the 27th player to reach world number one and only the third Russian, joining Yevgeny Kafelnikov (1999) and Marat Safin (2000-01).

The last player outside of Djokovic, Nadal, Federer and Britain's Andy Murray to sit atop the rankings was American Andy Roddick in February 2004.