Sevastova, who avenged last year's quarter-final loss to Stephens in NY to reach her first Grand Slam semi, converted five of her eight break points and saved seven of the nine against her on the Arthur Ashe Stadium court.
Indeed, the American has enjoyed the better of this rivalry to date, winning all three of their meetings - including a tie at the French Open earlier this year.
"Shocking, my first top-10 win", said Williams, who will face Anastasija Sevastova for the first time for a place in the final after the 19th seeded Latvian knocked out defending champion Sloane Stephens, the world number three.
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. It would be Williams' first major since she won the 2017 Australian Open.
"So the fact that I made it to the quarter-finals and played some really good matches and I just competed as hard as I could, I mean [there's] a lot to be proud of". "I'm just on my way (back) on the tour and doing the best I can".
Following a harrowing childbirth in September of a year ago, Williams suffered a pulmonary embolism which consequently caused the wound from her C-section to open up. She struck three aces in her first two service games and was quickly up two breaks on Pliskova.
Her sluggish start against Pliskova came in the same 90-degree heat and 50-per cent humidity that hampered John Isner in his quarterfinal loss to Juan Martin del Potro on Tuesday afternoon, and Roger Federer in his fourth-round exit against John Millman a night earlier and prompted the tournament to suspend play in junior matches for a few hours. "Right now you're so in the tournament and you don't feel it".
Next up for the 28-year-old is Serena, who beat Pliskova later in the day to move into the semis.
Sevastova broke the 25-year-old American's serve twice in the opening set, then broke her again to take a 2-0 lead in the second.
Alyssa Roenigk is a senior writer for ESPN The Magazine and ESPN.com whose assignments have taken her to six continents and caused her to commit countless acts of recklessness.
"I still know that no matter whether I'm in the semi-finals or the finals, I have a really long way to go to win that". Having achieved as much as Williams might make anyone complacent and a fan may not even have blamed her for hanging up her racquet - after all, she has more than proved her status as the Greatest of All Time.
Pliskova's game began to fall apart as Serena consolidated the break with her sixth and seventh ace while she skewed a poor backhand into the tramlines on break point and found herself 4-0 down looking like a woman who knows defeat is inevitable. I think she's still the strongest.
Keys: 'I felt good today.
"She's playing with the same power".
"She's 17, but she's not a player which should be 17", Pliskova said.
A child has been killed in Florida after a tree was blown on top of his mobile home in an incident which may be linked to Gordon. Brandon Drake, a meteorologist for the National Weather Service in Topeka, said theories differ on how the storm will progress.
Saturday morning, forecasters predicted the system would not form until it passed over Florida and entered the Gulf. Given Florence's remote location, the storm won't be near any areas of land through at least the weekend.
Radebe said that the fuel price was driven by global factors - such as the rand exchange rate, the worldwide price of crude oil. If the current trend continues, both petrol and diesel prices will have a double digit price growth in the current fiscal year.
He said he had heard reports that Damascus had set a September 10 deadline for diplomacy to work before attacking. Iranian Foreign Minister Mohammad Javad Zarif said on Monday that terrorists should be "cleaned out" of Idlib .
Michael Capuano (D-MA) conceded to Boston City Councilwoman Ayanna Pressley after polls closed in the state. Pressley defeated Capuano by arguing that it was time for a change in representation in the district.
Del Potro - the 2009 victor of the men's singles at Flushing Meadows - breezed past Borna Coric in the final match of the day. Serena, seeded 17th, routed Venus 6-1, 6-2 in matching the most-lopsided victory in the Williams sisters' series.
Thomas' reaction to the lack of a resolution was clear in his post: "The disrespect has been noted and will not be forgotten". Thomas has since reported to the Seahawks, but he still doesn't appear to be thrilled with his situation.
That was the first career Grand Slam final for Keys, who was one of four American women in the semifinals a year ago at the U.S. Former world No. 1 Novak Djokovic will be back on Arthur Ashe in prime time, facing American Tennys Sandgren.
But Pyongyang has since slammed Washington for its "gangster-like" demands for complete, verifiable and irreversible disarmament. Despite Trump's all-caps tweet from April - "KOREAN WAR TO END!" - that hasn't yet happened.
Kaia Kanepi of Estonia congratulates Serena Williams at the net after their match during the seventh day of the US Open. But having taken her first set against Williams in five career meetings, there would not be a second.
The initial image, announced through Rovell, has a close up of Kaepernick's face with the caption: "Believe in something . Colin Kaepernick is not on an National Football League roster, but he does have his own ad campaign, courtesy of Nike .
Nishikori takes revenge on Cilic
Kei Nishikori is headed to the US Open semifinal following a dramatic upset victory over Marin Cilic on Wednesday. Keys said she will look to home support on Thursday when she resumes her rivalry with Osaka.
Amazon Hits $1 Trillion Valuation
Amazon has become the second publicly traded company to be worth US$1 trillion (NZ$1.52 trillion), hot on the heels of Apple . Amazon has briefly become the second US-listed firm to have a market value of more than $1 trillion (£779bn).
John Millman Just Knocked Off Roger Federer At The US Open
The 13-times grand slam victor had made easy work of the opening set, breaking Sousa twice, the second time to close out the set. Kei Nishikori , runner-up in 2014, was also pleased to get through in three sets in blazing sunshine on Louis Armstrong Stadium.
McEnroe: Don't penalise umpire for Kyrgios pep talk
From the coach, to the physio to maybe even a counsellor, these are the people you hire to get the best out of you. De Minaur took the opening two sets, including a bagel in the second, before Tiafoe fought back to make it 2-1.
Tropical Storm Gordon drenches South Florida
The system was lashing Florida with tropical-storm-force winds and heavy rains Monday morning, according to the hurricane center. At the time, peak sustained winds were 45 miles per hour , but wind gusts were in the 50 mph-to-60 miles per hour range.
Is Steven Gerrard smart enough to outfox his old boss?
The victor came after 62 minutes when Olivier Ntcham swept home to find the net at the end of a swift counter attack. A fuming Gerrard told Sky Sports: 'It's definitely a foul. "I have seen it again five times and it is a foul".