MEMPHIS, Tennessee (AP) Top-seeded Kei Nishikori was pushed to three sets in his opening match of the Memphis Open on Wednesday, beating American qualifier Ryan Harrison 3-6, 6-3, 6-4 to advance to the quarterfinals.
Nishikori, the two-time defending champion from Japan who had a bye in the first round, struggled in the opening set against Harrison, who was playing his fifth match in five days. After steadying his play, he jumped to a 4-0 lead in the second set. In the third, he broke Harrison early and each held their serve through the rest of the match.
''The third set was a tight game, but I got the first game break, and that helped mentally,'' Nishikori said. ''I was a little more loose.''
Earlier Wednesday, fifth-seeded Ivo Karlovic, the runner-up in 2014, was eliminated by qualifier Austin Krajicek 7-6 (4), 4-6, 6-4.
Also, Sam Querrey defeated wild-card entry and fellow American Jared Donaldson 6-4, 6-1 in a match that took less than an hour.
In the final singles match of the day, third-seeded John Isner defeated Ivan Dodig of Croatia. 6-4, 7-6 (5). The hard-serving American used 22 aces combined with only one double fault to overcome Dodig. Isner will face close friend Querrey in the quarterfinals. Querrey won the 2010 championship in Memphis, defeating Isner in the finals
Karlovic, who won his opening match with 23 aces, recorded 32 in the three sets against Krajicek, but only seven of those came in the deciding set, when the Croatian also double faulted seven times.
For Krajicek, it marked only his third win on the ATP tour, and set him up to face Nishikori in the quarterfinals.
Nishikori said there wasn't anything in particular that caused the slow start against Harrison.
''He played to a good level,'' Nishikori said. ''The first set I wasn't really ready for the match. The second set, I started playing better and stepping in a little more. I was more aggressive.''
The aggressiveness showed with the fifth-ranked player in the world coming to the net and running Harrison from side to side on extended points.
''I was coming in a little more because he was hitting a little slice.'' Nishikori said, ''and he has great defense. I knew I had to sneak in a couple of times.''