Defending champion Kei Nishikori won his 14th consecutive match at the Memphis Open when he beat Ryan Harrison 6-2, 7-5 on Wednesday.
Coming off a quarter-final loss to world number one Novak Djokovic at the Australian Open, Nishikori began his title defence by breaking Harrison twice in the first set en route to clinching it 6-2.
After facing little difficulty in the first set, Nishikori was pushed hard by Harrison in the second set even though the world number seven broke the American to take a 4-2 lead.
Harrison fought his way back into contention and saved four match points in the 10th game to draw level at 5-5.
However, Harrison’s efforts were in vain as Nishikori broke him in the next game before going on to book his spot in the quarter-finals.
Nishikori will face Mikhail Kukushkin in the last eight after the man from Kazakhstan upset fifth seed Denis Kudla 6-1, 7-5.
Meanwhile, fourth seed Sam Querrey and Japanese qualifier Yoshihito Nishioka also progressed to the quarter-finals.