Rafael Nadal retains top spot in the battle with Novak Djokovic for the year-ending number one in the ATP tennis rankings. Photo: Kamil Zihnioglu/AP Photo

BERLIN  Rafael Nadal retains top spot in the battle with Novak Djokovic for the year-ending number one in the ATP tennis rankings.

Djokovic began his campaign to reclaim the world number one spot with a 6-2, 6-1 win over Italy's Matteo Berrettini at the ATP Finals in London on Sunday.

Nadal was in action late Monday against Germany's Alexander Zverev.

Djokovic must at least reach the final at London's O2 Arena with two round robin successes if he is to overtake Nadal and equal American Pete Sampras' record of six year-end number one finishes.

The only movement in the rankings released Monday was outside the leading 30.

1. (1) Rafael Nadal, Spain, 9,585 points 2. (2) Novak Djokovic, Serbia, 8,945 3. (3) Roger Federer, Switzerland, 6,190 4. (4) Daniil Medvedev, Russia, 5,705 5. (5) Dominic Thiem, Austria, 5,025 6. (6) Stefanos Tsitsipas, Greece, 4,000 7. (7) Alexander Zverev, Germany, 2,945 8. (8) Matteo Berrettini, Italy, 2,670 9. (9) Roberto Bautista Agut, Spain, 2,540 10. (10) Gael Monfils, France, 2,530

dpa