DUBAI: Top seed Kei Nishikori fell to a shock second round defeat at the Dubai Duty Free Tennis Championships on Wednesday, but Roger Federer came through his second three-set battle this week to record his 50th win in Dubai and reach his 11th quarter-final. Nishikori, the world No. 6, was defeated 7-5 5-7 6-2 by Hubert Hurkacz, who until last …