Nadal's first official ATP tour event for the year was the 250 series Qatar Open in Doha, where he lost in the quarterfinals to Gaël Monfils.
Nadal also entered and won the tournament's doubles event with partner Marc López, defeating the No.
1-ranked doubles team of Daniel Nestor and Nenad Zimonjić in the final.
At the 2009 Australian Open, Nadal won his first five matches without dropping a set, before defeating compatriot Fernando Verdasco in the semifinals in the second longest match in Australian Open history at 5 hours and 14 minutes.
This win set up a championship match with Roger Federer, their first meeting ever in a hard-court Grand Slam tournament.
Nadal defeated Federer in five sets to earn his first hard-court Grand Slam singles title, making him the first Spaniard to win the Australian Open.

At the ABN AMRO World Tennis Tournament in Rotterdam, Nadal lost in the final to second-seeded Andy Murray in three sets.
Although this knee problem was not associated with Nadal's right-knee tendonitis, it was serious enough to cause him to withdraw from the Dubai Championships a week later.
In March, Nadal helped Spain defeat Serbia in a Davis Cup World Group first-round tie on clay in Benidorm, Spain.
Nadal defeated Janko Tipsarević and Novak Djokovic.
At the 2009 Indian Wells Masters, Nadal won his thirteenth Masters 1000 series tournament, defeating Murray in the final.
The next ATP tour event was the 2009 Miami Masters.
Nadal advanced to the quarterfinals, where he again faced Argentinian del Potro, this time losing the match.

Nadal began his European clay court season at the Monte Carlo Masters, where he defeated Novak Djokovic to win a record fifth consecutive singles title there.
He then won back to back titles in Barcelona and Rome Masters, defeating Ferrer and Djokovic respectively.
He then surprisingly lost the final of the Madrid Open to Roger Federer.
This was the first time that Nadal had lost to Federer since the semifinals of the 2007 Tennis Masters Cup.

By beating Lleyton Hewitt in the third round of the French Open, Nadal set a record of 31 consecutive wins at the French Open, beating the previous record of 28 by Björn Borg.
This run came to an end on 31 May 2009, when Nadal lost to eventual runner-up, Robin Söderling in the 4th round.
This was Nadal's first and, until 2015, only loss at the French Open.
After his surprise defeat in France, Nadal withdrew from the AEGON Championships.
It was confirmed that he was suffering from tendinitis in both of his knees.
On 19 June, Nadal withdrew from the 2009 Wimbledon Championships, citing his recurring knee injury.
Roger Federer went on to win the title, and Nadal consequently dropped back to No.
2 on 6 July 2009.

On 4 August, Toni Nadal confirmed that Nadal would return to play at the Rogers Cup in Montreal.
There, he lost in the quarterfinals to Juan Martín del Potro.
With this loss, he relinquished the No.
2 spot to Andy Murray on 17 August 2009, ranking outside the top two for the first time since 25 July 2005.

At the US Open Nadal fell in the semifinals, losing to eventual champion Juan Martín del Potro.
At the World Tour Finals, Nadal lost all three of his matches against Robin Söderling, Nikolay Davydenko, and Novak Djokovic respectively without winning a set.
In December, Nadal participated in the second Davis Cup final of his career.
He defeated Tomáš Berdych in his first singles rubber to give the Spanish Davis Cup Team their first point in the tie.
After the Spanish Davis Cup team had secured its fourth Davis Cup victory, Nadal defeated Jan Hájek in the first Davis Cup dead rubber of his career.

Nadal finished the year as No.
2 for the fourth time in five years.
Nadal won the Golden Bagel Award for the third time in 2009, with nine 6–0 sets during the year.
Nadal's first official ATP tour event for the year was the 250 series Qatar Open in Doha, where he lost in the quarterfinals to Gaël Monfils. Nadal also entered and won the tournament's doubles event with partner Marc López, defeating the No. 1-ranked doubles team of Daniel Nestor and Nenad Zimonjić in the final. At the 2009 Australian Open, Nadal won his first five matches without dropping a set, before defeating compatriot Fernando Verdasco in the semifinals in the second longest match in Australian Open history at 5 hours and 14 minutes. This win set up a championship match with Roger Federer, their first meeting ever in a hard-court Grand Slam tournament. Nadal defeated Federer in five sets to earn his first hard-court Grand Slam singles title, making him the first Spaniard to win the Australian Open.
At the ABN AMRO World Tennis Tournament in Rotterdam, Nadal lost in the final to second-seeded Andy Murray in three sets. Although this knee problem was not associated with Nadal's right-knee tendonitis, it was serious enough to cause him to withdraw from the Dubai Championships a week later. In March, Nadal helped Spain defeat Serbia in a Davis Cup World Group first-round tie on clay in Benidorm, Spain. Nadal defeated Janko Tipsarević and Novak Djokovic. At the 2009 Indian Wells Masters, Nadal won his thirteenth Masters 1000 series tournament, defeating Murray in the final. The next ATP tour event was the 2009 Miami Masters. Nadal advanced to the quarterfinals, where he again faced Argentinian del Potro, this time losing the match.
Nadal began his European clay court season at the Monte Carlo Masters, where he defeated Novak Djokovic to win a record fifth consecutive singles title there. He then won back to back titles in Barcelona and Rome Masters, defeating Ferrer and Djokovic respectively. He then surprisingly lost the final of the Madrid Open to Roger Federer. This was the first time that Nadal had lost to Federer since the semifinals of the 2007 Tennis Masters Cup.
By beating Lleyton Hewitt in the third round of the French Open, Nadal set a record of 31 consecutive wins at the French Open, beating the previous record of 28 by Björn Borg. This run came to an end on 31 May 2009, when Nadal lost to eventual runner-up, Robin Söderling in the 4th round. This was Nadal's first and, until 2015, only loss at the French Open. After his surprise defeat in France, Nadal withdrew from the AEGON Championships. It was confirmed that he was suffering from tendinitis in both of his knees. On 19 June, Nadal withdrew from the 2009 Wimbledon Championships, citing his recurring knee injury. Roger Federer went on to win the title, and Nadal consequently dropped back to No. 2 on 6 July 2009.
On 4 August, Toni Nadal confirmed that Nadal would return to play at the Rogers Cup in Montreal. There, he lost in the quarterfinals to Juan Martín del Potro. With this loss, he relinquished the No. 2 spot to Andy Murray on 17 August 2009, ranking outside the top two for the first time since 25 July 2005.
At the US Open Nadal fell in the semifinals, losing to eventual champion Juan Martín del Potro. At the World Tour Finals, Nadal lost all three of his matches against Robin Söderling, Nikolay Davydenko, and Novak Djokovic respectively without winning a set. In December, Nadal participated in the second Davis Cup final of his career. He defeated Tomáš Berdych in his first singles rubber to give the Spanish Davis Cup Team their first point in the tie. After the Spanish Davis Cup team had secured its fourth Davis Cup victory, Nadal defeated Jan Hájek in the first Davis Cup dead rubber of his career.
Nadal finished the year as No. 2 for the fourth time in five years. Nadal won the Golden Bagel Award for the third time in 2009, with nine 6–0 sets during the year.
Rafael Nadal