Top seed Kei Nishikori extended his winning run at the Memphis Open to 14 matches with a 6-2 7-5 victory over American Ryan Harrison.
Three-time champion Nishikori reeled off five games in a row on his way to securing the first set inside 27 minutes and Harrison broke for the first time in the match with Nishikori looking to serve out at 5-4.
But NIshikori broke straight back before closing out the match and told the ATP's official website: "I had easy mistakes and should have closed it out but happy to finish the last two games.
"I was actually playing very good, very solid today. The last two games were a bit of a struggle. Usually I struggle the first couple of rounds here so this is the best start so far."
Nishikori will play Kazakhstan's Mikhail Kukushkin in the quarter-finals after he best the number five seed Denis Kudla 6-1 7-5.
Fourth seed Sam Querrey eased through with a 6-3 6-4 win over Henri Laaaksonen and qualifier Yoshihito Nishioka also advanced after beating Illya Marchenko 6-1 6-3.
Source: PA
