London: Novak Djokovic began his quest for a record-equalling sixth ATP Finals title and sixth year-end number one spot on Sunday with an imperious 6-2, 6-1 victory against Italy's Matteo Berrettini.
The Serbian was last week nudged off the top position in the rankings by Rafael Nadal, who is also in the eight-man field in London.
Djokovic must reach the final at the O2 Arena to stand any chance of dislodging Nadal but there are major questions over the Spaniard's fitness. If the Serbian does claim the year-end number one ranking for a sixth time, he would match the record of Pete Sampras.
