Djokovic romps to victory in ATP Finals opener

Novak Djokovic won his opening match at the ATP Finals AFP/Adrian DENNIS

The Serbian, a five-time champion at the end-of-season event, was last week nudged off the top spot in the rankings by Rafael Nadal, who is also in the eight-man field in London.

Djokovic, who won the Australian Open and Wimbledon this season, must reach the final to stand any chance of dislodging Nadal but there are major questions over the Spaniard's fitness.

The second seed saw off the challenge of Berrettini in just 62 minutes, converting five of seven break points and out-serving his 23-year-old opponent.

Eighth-seed Berrettini, appearing at the ATP Finals for the first time, went toe to toe with Djokovic at the start of the match but the Serbian broke twice to take the first set 6-2.

Djokovic romped into a 4-0 lead in the second set as the Italian continued to struggle with his serve but was pegged back in the fifth game as Berrettini broke for the first time.

The unflappable 16-time Grand Slam champion broke back in the following game and served out to take the set 6-1.

Germany's Alexander Zverev shocked Djokovic in last year's final at the O2 Arena but the Serbian is the firm favourite to equal Roger Federer's tally of six ATP Finals titles after cantering to victory at last week's Paris Masters.

Federer, Nadal and Djokovic were the top three seeds when they first competed together at the tournament way back in 2007 and are still the men to beat 12 years later.

Nadal, who has never won the event, is bidding to clinch the year-end number one spot in the ATP rankings for a fifth time.

The season-ending tournament, featuring the year's best eight players, is contested in a round-robin format with the best four players and doubles teams reaching the knockout semi-finals stage.

The other two members of the Bjorn Borg group are Federer and Dominic Thiem of Austria, who meet in the evening match.

Nadal, Daniil Medvedev, Stefanos Tsitsipas and Zverev are in the Andre Agassi group.