![Confident: Kei Nishikori.](/web/20161114235007im_/http://www.theage.com.au/content/dam/images/g/s/p/b/a/z/image.related.wideLandscape.460x259.gsp9p3.png/1479157788665.jpg)
Nishikori starts with a win, Wawrinka vows to rebound
One is not the only sought-after rankings number at this week's Barclay ATP World Tour Finals, with a trio of contenders vying to fill the rare year-end position in the top three vacated by the absent Roger Federer.