Angelique Kerber made sure there would not be another slipup against Naomi Osaka on Monday as the former U.S. champion eliminated the local favorite in straight sets in the first round of the Toray Pan Pacific Open.

Kerber, who was beaten in the first round by the 19-year-old Osaka as defending U.S. Open champion last month, returned the favor to the new face of Japanese women's tennis, winning 6-3, 6-4 at Ariake Colosseum.

Apart from her brief lead in the second set, Osaka, who lost to Caroline Wozniacki in the final at last year's tournament, was largely kept at bay by Kerber, the world No. 14 and the seventh seed.

Osaka could only manage to connect on 54 percent of her booming first serves, and was outaced by her German opponent five to three, breaking Kerber just once during the 83-minute match.

"I feel like she played really good," Osaka said of Kerber, who will face either Caroline Garcia of France or Russia's Daria Kasatkina in the second round. "I was actually having a lot of fun playing her, especially since we were playing in Tokyo."

"It was just the last three games were kind of really bad, I don't really know why."

Osaka's Japanese homestand was not a good one, lasting just two matches in two weeks, with a first-round exit last week at the Japan Women's Open. She said there was no pressure playing at home nor from expectations to reproduce her triumph in New York last month.

"I didn't really feel pressure because I kind of went through that already in the first tournament I played here," said Osaka, ranked 46th in the world. "I didn't feel pressure because I know I'm going to play a lot of matches here in the future."

"People play certain players a lot. I know that once you're a top player, you tend to play the same opponents a lot because that's just how the draw is. I thought it was kind of interesting I was playing her again so soon."

"I don't feel like she changed that much."

Kerber echoed Osaka's sentiments, saying she essentially tried to hone her game and not alter it from the U.S. Open, where Osaka won in a swift 65 minutes.

"I was talking with my coaches today and we were trying to figure out what I can do better than last time," Kerber said. "For me, it was more important to look on my side of the court."

"I knew what to expect after the last match a few weeks ago. If she hits the first serve, it's really fast and I was expecting that. I was ready to hit the fast balls back at her."

"I was trying to play my game better than last time."

Kerber broke Osaka to take a 2-1 lead in the first set and never looked back, forcing her teenage opponent into mistakes and keeping her from finding her groove.

Osaka seemed to have figured it out in the second set, breaking Kerber for the first -- and only, as it turns out -- time in the fifth game to go up 4-2 after the sixth.

But a resilient Kerber won the ensuing four games as a frustrated Osaka hit long to set up match point for the German. Osaka shot beyond the baseline again to hand victory to Kerber, who was relieved to be going through amid sighs all around from the crowd.

Osaka's only opponent at the Japan Women's Open, compatriot Kurumi Nara, shook off a rocky first set to oust Yulia Putintseva of Kazakhstan in three sets on Monday.

Nara, the world No. 108, won 2-6, 6-4, 6-2 to advance to the second round, where she was eliminated at last year's tournament. Nara said she found Putintseva slightly difficult because of their similar styles.

Nara, who fell at the second hurdle of last week's Japan Women's Open, barely showed up in the first set against the 52nd-ranked Putintseva, who had led their career matchups 3-1.

The second set looked to be more of the same after Putintseva moved in front 3-1. But Nara began plotting her comeback as she held serve in the fifth game before breaking Putintseva in the sixth to make it three games apiece.

Putintseva's first serve completely abandoned her in the set at 48 percent accuracy and she could only turn 39 percent of her second serves into points. She managed to break right back but Nara won the next three games, forcing a third set.

After Nara converted set point, Putintseva threw her racket to the ground in a fit of frustration and the unraveling continued in the final set.

Nara jumped out to a 4-0 lead and while Putintseva pulled two games back, the Kazakhstani regained her composure too late. Nara finished off her in the eighth game, pouncing on the first match point she saw.

In one other first-round match, China's Wang Qiang barely broke a sweat in dismissing Kristina Mladenovic of France 6-0, 6-0.

Meanwhile, organizers announced that Agnieszka Radwanska, a two-time tournament champion, has pulled out due to a virus. The 11th-ranked Pole was seeded sixth, and would have faced Nara had she won in the first round.