Novak Djokovic inspired Serbia to win the first ATP Cup when his win over Rafael Nadal helped his country beat Sydney 2-1 in Spain.
Number two in the world, Djokovic (32), defeated Nadal (33) 6-2 (7-6) (7-4) after Roberto Bautista defeated Agut Dusan Lajovic 7-5 (6-1).
Djokovic linked Viktor Troicki with a 6-3-6-4 double victory against Pablo Carreno Busta and Feliciano Lopez.
"I will remember this experience for the rest of my life," said Djokovic.
"It is definitely one of the best moments in my career."
Djokovic and Troicki quickly dropped 3-1 in the first set of the double, but the lively Serbian couple won the next five games to reach the first set.
They broke early in the second and kept their momentum when Djokovic stopped the match on his first attempt.
Djokovic, the reigning Australian Open champion, lost no match during the week-long tournament and won six singles and two doubles.
"It was an enormous team effort," said Djokovic.
"I was very happy and lucky to have had a great career, but playing with some of my best friends for your country cannot be matched."
The Australian Open will begin on January 20, eight days after the ATP Cup ends.
Nadal is frustrated by the crowd
Nadal has now lost his last nine hard court games against Djokovic, who had hardly any problems in the opening set.
The Spaniard was broke in the first game of the game and was visibly frustrated by the pro-Serbian crowd when he dropped the serve.
Djokovic served the first set, but was tested harder in the second and saved five breakpoints in a 10-minute service game.
Nadal secured two breakpoints with two wins in a row, but Djokovic took control of the tie break and ended the win when Nadal sent a forehand into the net.
"There should be respect for both players," said Nadal to the crowd afterwards.
Nadal won the Davis Cup with Spain six weeks ago. This is a similar format to the ATP Cup and he believes the two events are too close together.
"I think that [scheduling] This is confusing for the audience and we have to be clear in our sport, "he added.
"And for the health of our sport and for the good of our sport it is imperative that we repair it."