LONDON (Reuters) - London’s last edition of the ATP Finals opened on Sunday with a repeat of last year’s final but this time Dominic Thiem prevailed against Greek defending champion Stefanos Tsitsipas.Rafa Nadal, bidding to claim the only major title to elude him, starts his challenge later against Russian debutant Andrey Rublev in the day’s other London Group match. “It was a tough match, both of us served well and conditions were fast,” Austrian Thiem, playing at the elite year-ender for the fifth time in succession, said on court. “I know how important it is to have a good start in the first match here.” The ATP Finals, in its 50th edition, is being staged in London’s O2 Arena for the 12th and last time before it moves to Turin and sadly plans for a vibrant farewell party in front of the usual sell-out crowds has been scuppered by the COVID-19 pandemic. The cavernous arena, which holds close to 20,000 people in tournament set-up, was dark and empty as the players walked on court to the usual fanfare and music.