Andy Murray's hopes of finishing his season on a high were dealt a serious blow as he fell to a straight-sets defeat by Kei Nishikori of Japan.
The Scot only made the end-of-season tournament thanks to a late run of superb form but world No.5 Nishikori outfought a tired-looking Murray to claim a 6-4, 6-4 victory in London's O2.
The defeat puts Murray's back against the wall when it comes to qualifying for the next round from Group B. He must face Roger Federer and Milos Raonic and realistically needs victories in both matches to progress.
