But Stephens clawed her way back and screamed when Pliskova's forehand went wide to give her a first game after just over 50 minutes of play.
"I've just got one more to go".
From there Stephens found her footing and seventh-seeded Pliskova began to derail.
Stephens was the first to settle, winning the first three games en route to a 6-3 first-set success. I was, like, I'm going to lose 0-0. I'm trying so hard but nothing's working.
"But after I won the first game there was a rush of adrenalin and I told myself that if I could win one game, then I could win another".
The 24-year-old has never progressed beyond the quarter-finals of a Grand Slam but is determined to build on her Singapore conquest, which also included defeating defending champion Caroline Wozniacki.
Stephens gifted Pliskova an immediate break back by sending a lazy backhand long, but a double fault returned the initiative to the world number six and she held firm to force a decisive set.
Pliskova was only a point away from a 3-0 lead in the second set.
"After the US Open previous year, everyone was, like, 'Oh, she's a one-hit wonder, she'll never do anything again, it was just lucky, no one was playing, blah, blah, blah, '...this season I was like 'I really want to play a little more consistent, I want to have some better results in the bigger tournaments and just do better to show that I'm a Top 10 or top-whatever player".More news: Pipe Bomb Suspect Set for First Court Appearance in Florida
Ukrainian tennis player Elina Svitolina in a rather tense match was won by Kiki, Bertens and reached the final of the WTA tournament in Singapore.
Svitolina charged, got to the ball and dropped it neatly across the net to win the point and the game.
"I just made a couple extra plays on the ball".
"There's still lots of work ahead", said sixth-seeded Svitolina.
Svitolina added: "I was clear with what I had to do on court".
This is the first year since 2011 that Serena Williams didn't win a major title, and she's 37 years old now. "I definitely know what she's talking about".
Bertens only qualified for the WTA Finals just days before the tournament after world number one Simona Halep withdrew due to injury. However, to win the set, she failed on a tie-break niderlandy won 7:5.
Bertens said Svitolina's defensive skills forced her into playing ultra-aggressive.
Next up for Svitolina will be the victor of the other semifinal match between Sloane Stephens of the United States and Karolina Pliskova of the Czech Republic.
Elina Svitolina of the Ukraine, right, greet by Kiki Bertens of the Netherlands after their women's singles semi final match at the WTA tennis finals in Singapore, Saturday, Oct. 27, 2018.