"But I think I totally understand, and I think that to go play at home in Tokyo was really important for her or her fans, for her country".
Osaka changed her tactics at the start of the second set, drawing Stephens way from her baseline comfort zone to hold far more comfortably.
The three-time major victor appeared to increase her command on proceedings when she broke Bertens at the start of the second set but her 26-year-old opponent hit back to break twice to force a third set.
There Osaka's momentum ended, as she swiftly found herself 1-4 down to a more inspired Stephens.
Two more unforced errors into the net by Osaka gave Stephens a triple break point in the next game and caused Osaka to swing her racket violently toward the court in frustration. Osaka was broken on seven of 19 break-point opportunities, while Stephens was broken on four of 12.
"So I think that the fact that you get another chance to learn from your mistakes and apply it in the matches going on is something that's really good".
"Yeah, I think it's really cool that you can keep going even after you lose". Obviously playing someone with a lot of confidence is always a tough task, but I think that I played well, and I kept a good attitude. And this is really interesting because all the players you play here are the best in the world. So I was pleased with that.
"It's been one match", said a smiling Stephens, who notched her third win in Asia last night - she had lost in the opening rounds of the Tokyo and Wuhan Opens, and in the round of 16 at the China Open in Beijing. "It was a slow start but I was really happy to turn around this match". "Hopefully for the next match I can go out there, play a little bit more like how I want to play", she added.
It was followed by another marathon match with number eight seed Kiki Bertens overcoming top-seed Angelique Kerber in a thrilling 1-6, 6-3, 6-4 comeback victory.
Stephens won the pair's only previous match two years ago in Acapulco.
The Japanese said: "If you think you hit a victor, she'd still run for it and it feels like you have to restart the point from zero".
Bertens' victory not only secured the Dutchwoman a memorable win on her WTA Finals debut, but it also ensured that for the first time in the tournament's round-robin format, all four lower seeds recorded wins in the first round of mathces.
"I had a little chat with my coach when it wasn't going so well, so we chose to go a little bit more for my shots, play a little more aggressive and it worked out".