Defending champion Novak Djokovic beat top-ranked Rafael Nadal 6-3, 6-4 to win the ATP World Tour Finals on Monday, extending his winning streak to 22 matches and claiming the elite season-ending title for the third time.

Djokovic, who has not lost a match since his defeat to Nadal in the U.S. Open final, returned superbly from the start to move his Spanish rival around the court and prevent him from dictating the points.

Nadal hit only nine winners and was broken three times in a match between the two dominant players of the season.

Nadal replaced Djokovic for the No. 1 ranking last month, but the Serbian player proved again he still has the upper hand on hard courts by extending his head-to-head winning record to 13-7 on that surface.

Djokovic made an impressive start, hitting powerful groundstrokes to keep Nadal well behind his baseline while limiting his own mistakes. Returning well, the Serb made the most of two of Nadal's backhand errors to break in the second game. He had another chance in the fourth game after Nadal double-faulted, but was unable to convert.

Nadal got into the match from that point. He put Djokovic under pressure with his huge forehands in the next game and two unforced errors from the Serb allowed him to break back and then level at 3-3.

But Nadal faltered in his next service game as he served a double-fault at 30-30. After a stunning exchange, Djokovic broke for 5-3 following a series of volleys at the net. Standing in the middle of the court, the Serb opened his arms and screamed as the crowd erupted in cheers.

Djokovic sealed the first set with an ace.

Looking supremely confident, Djokovic raised his game further in the second set, pinpointing his shots on the lines to make life more difficult for Nadal after breaking in the third game of the second set.

The resilient Spaniard saved two match points and kept encouraging himself until the end, but a final forehand too long gave Djokovic the title. (AP)