BUENOS AIRES, Argentina — Hiring Andy Murray as his coach came naturally for Novak Djokovic. On a trip to Argentina to play in a farewell match for Juan Martín del Potro, the Serbian explained why he chose his former rival after being without a coach for six months.

Murray and Djokovic announced last week they plan to work together for the Australian Open in January.

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“Since I was very young, I have played against him… and there are not many people who have won multiple Grand Slam titles,” said Djokovic in Spanish in a press conference before the match against Del Potro.

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Djokovic is a 24-time Grand Slam champion who has spent more weeks at No. 1 than any other player in tennis history. Murray won three major trophies and two Olympic singles gold medals and finished 2016 atop the ATP rankings. He ended his playing career after the Paris Olympics in August.

Both men are 37 and were born a week apart in May 1987. They started facing each other as juniors and wound up meeting 36 times as professionals, with Djokovic holding a 25-11 advantage.

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“He knows my game and everything that I have been through very well,” added Djokovic, currently No. 7 in the ATP rankings. “He knows the things that are wrong with my game, all of my mistakes.”

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Djokovic has been without a full-time coach since splitting in March from Goran Ivanisevic.

Del Potro, who won the US Open in 2009, won the exhibition match played in Parque Roca, Buenos Aires, 6-4, 7-5.

“We played against each other in the biggest stages of our sport, but in the end our friendship was bigger than the rivalry,” added Djokovic. “We are here to celebrate Juan Martin’s career and to enjoy every moment.”