Stephens beat Sevastova in the same round previous year en route to her first grand slam title, but she missed numerous chances to grab an early lead in the rematch and could never get back into the match.
Williams would rattle off eight wins a row, going up 4-0 in the second set, before Pliskova ended her streak and won the next two games.
The six-time USA champion won eight games in a row - four at the end of the first and four at the start of the second - to help her secure victory in one hour 26 minutes.
"I was playing really not a good game", Williams, who was a point from trailing by two break in the opening set, said. "You just have to go with it", Stephens said.
In the semi-finals, Williams will take on Latvia's world number 19, Anastasija Sevastova. Williams missed the 2017 edition as she gave birth to her daughter, Alexis Olympia.More news: Elon Musk smokes marijuana during podcast
It was a very different story from their last encounter in NY, as Pliskova upset the six-time champion on the way to so far her only Slam final.
"When I get to a Grand Slam, I feel I want to play really hard".
Nadal will face 2009 champion Juan Martin del Potro next, with the 2009 champion having outslugged John Isner 6-7 (5-7), 6-3, 7-6 (4-7), 6-2 to reach the last four. Williams then cashed in a break point to level the set at 4-4 when Pliskova hit a backhand into the net. "She was No. 1 a year ago, so she got there for a reason".
The 28-year-old ultimately converted her third match point to advance to her first Grand Slam semifinal.
The world number 26 got off to a slow start against her Czech opponent, serving up a host of double faults and errors, which the eighth seed Pliskova capitalised on to race into a 3-1 lead. Aside from Williams' coach, Patrick Mouratoglou, who has been saying since her first match at Indian Wells that she will win a Slam this season, no one was making bold predictions for her play in NY.
"I'd been a couple steps away at the last Grand Slam, so I'm definitely not ahead of myself", said Williams, the memory of a 6-3 6-3 loss to Angelique Kerber in the Wimbledon final still fresh.More news: USA has seen evidence of Syria preparing chemical weapons in Idlib -envoy
Pliskova got another chance when Williams batted a forehand into the net, but another booming serve, a backhand victor and an unreturnable serve saw her negotiate the danger.
"So now I feel like I'm at a level where I can play and try to compete against these awesome women in the Top 10".
"He's a close friend on tour, a great guy and I wish him the very best. he is young and has plenty of time to win tournaments". A strong response from Williams as Pliskova continued to fight back made it 5-2 before putting the final touches on the win.
"I've seen her play a lot".
She could be ranked as high as 11th by the end of play Saturday, should she make 2018 her seventh US Open crown.More news: Sacha Baron Cohen sued for $95m by Roy Moore