Rafael Nadal wins in Madrid as injury forces Kei Nishikori to retire - CNN
Nadal wins Madrid Open after Nishikori retires - SI
Kei Nishikori injury lets Rafael Nadal off the hook in Madrid Open - The Guardian
Rafael Nadal wins Madrid Open title when Kei Nishikori retires- LATimes
Rafael Nadal clinches Madrid Open title - InDepth IExpressRafael Nadal wins 4th Madrid title - ESPN Nadal d. Nishikori - Tennis.com