The Belarusian underestimated her opponent in their previous two meetings last year, when Pliskova defeated her in the Wimbledon and Montreal semi-finals but was in dominant form in New York as she fired down seven aces and never dropped serve.
"Today I expected a great level," Sabalenka said in an on-court interview. "I just tried to stay in this match as long as I can."
Nothing went right for 2016 finalist Pliskova during the first set as she racked up 15 unforced errors and five double faults in 28 minutes.
But the Czech's form improved considerably in the second set as she fended off the only break point she faced in the eighth game.
Sabalenka kept her cool in the tiebreak and raised her arms in triumph after sealing victory with a forehand winner on her second match point.
"Right now I'm not going for aces I'm just trying to put my serve on the big targets," she said.
"I'm ready for another fight and I think I just have to stay focused on myself."
Sabalenka will play either world number one Iga Swiatek (21) or Jessica Pegula (28), the last American left in the women's draw, for a place in Saturday's final.
Wimbledon ban gave her extra motivation for New York
Wimbledon's decision to ban Belarusian athletes from this year's grasscourt major gave Sabalenka extra motivation to do well at this month's U.S. Open.
Wimbledon organisers banned players from Russia and Belarus this year due to Moscow's invasion of Ukraine. Belarus is a key staging area for the invasion, which Russia calls a "special military operation". The players from the two countries were also blocked from competing in British grasscourt events in the build-up to the tournament.
"It was tough time, especially when I was working out in the gym and there was Wimbledon playing on the TV. I was always turning it off because I couldn't watch it," said Belarus's Sabalenka.
"But it was tough time, and I worked so hard."
Sabalenka reached the Wimbledon semi-final a year ago and is on the hunt for her first major title.
"They took away one opportunity from me and I worked really hard for this one," she told reporters.
The year's final major has not been immune to moments of political tension after US Open organisers allowed players from Russia and Belarus to compete, albeit under neutral flags - a move that was met with criticism from some Ukrainian athletes.
"It's tough and it's a lot of pressure," playing under geopolitical tensions, said Sabalenka.
"I'm just an athlete and I have nothing to do with politics. I'm just trying to play my best and make sure that people enjoy watching my matches."
