CINCINNATI, Ohio (Kyodo) -- Japan's Kei Nishikori made a second-round exit from the Western & Southern Open on Wednesday, losing in straight sets to former world No. 3 Stan Wawrinka.
The 2016 U.S. Open champion from Switzerland showed his game is back on track following a prolonged absence with a knee injury that saw his ranking tumble to 263 in June.
Wawrinka, 33, landed 60 percent of his first serves and lost just six of the 31 points in which he did so, allowing just one break in a 6-4, 6-4 win over 28-year-old Nishikori.
"At the start we saw the tennis I want to play, but midway through I gave up on hitting some balls and things went downhill from there," Nishikori said. "My opponent began playing better, and things turned for the worse."
"I want to get back to playing good tennis as soon as I can."
After both players held serve through the first three games of the opening set, world No. 23 Nishikori broke Wawrinka to take a 4-1 lead.
However, the Swiss won the next three games to draw level at 4-4, before earning three break points in the ninth game.
Nishikori fought his way back to deuce, but Wawrinka secured the break to go up 5-4 before serving out the set.
Wawrinka held serve throughout the second set and did not face a single break point as he booked his ticket to the round of 16.
The men's tournament in Cincinnati is one of nine ATP World Tour Masters 1000 events each season and serves as the final warm-up for the U.S. Open, the last Grand Slam of the year.
Former world No. 4 Nishikori reached the final of the U.S. Open in 2014 in his best-ever result at a Grand Slam.