Karolina Pliskova, the big-serving Czech who had already brushed aside a mounting reputation as a grand slam underachiever by making it to the US Open semi-finals, delivered a stunning display of power and composure to overwhelm top seed Serena Williams in the upset of the tournament on Thursday night.

An eerie hush fell over Arthur Ashe Stadium after Williams double-faulted on match point in the second-set tiebreaker, closing the show at 6-2, 7-6 (5) and ensuring Pliskova’s shock passage into Saturday’s final after 86 minutes. The outcome cost Williams not only a chance at a history-making 23rd grand slam title to eclipse Steffi Graf’s professional-era mark for major championships but also the No1 ranking that she’s held since February 2013 – a span of 186 weeks that equaled Graf’s record for consecutive weeks on top.

It marks the second straight year Williams has fallen at the penultimate hurdle in a bid for history at the season-ending major. Last September, a three-set loss to the unseeded Italian Roberta Vinci torpedoed her challenge for a calendar-year grand slam. On Thursday, the saboteur was a slender Czech all but unknown to casual observers due to her chronic underperformance in the early rounds of the sport’s four bedrock tournaments. Until now.

The matchup between the tour’s two best servers – Pliskova’s 446 aces are the most on the circuit this year while Williams exits with a tournament-high 65 – augured the hellfire that unfolded on a humid night at the world’s largest tennis stadium. The American kicked off proceedings with a 95mph ace out wide and held at love, but Pliskova responded with a 113mph missile down the middle in her opening service game.

The No10 seed drew first blood in the third game when she attacked a second serve with a vicious two-handed backhand that Williams couldn’t handle for 30-love. Her baseline power forced Williams into another error to earn a break-point chance, which she converted when Williams sent a backhand sailing past the baseline.

When Pliskova raced out to 40-love in the following game before consolidating the break on a Williams error, there was no evidence of the opening-reel nerves that had cost her the first set in Monday’s fourth-round win over Venus Williams. Instead the 24-year-old served confidently, was aggressive early in the rallies and went for winners.

“I was pretty calm today,” Pliskova said. “Before the match I felt a little bit like pressure, a bit nervous. But when I stepped on the court I didn’t feel anything. I just, you know, wanted to win, actually. Not just enjoy but to win.”

Serving at 1-3, Williams fell behind love-30 but fought back to stay within touching distance. She pushed Pliskova in the following game with the aid of two double faults, but the Czech served her way out of trouble. All night Williams struggled to read Pliskova’s serve as she hit all four corners of the service box, disguising the direction masterfully with her toss.

Williams, serving at 2-4, followed a double fault with three unforced errors and was broken at love. Pliskova calmly followed with a stress-free hold to take the first set in 26 minutes, winning 11 of the final 12 points as a near-capacity crowd buzzed with concern.

At that point Williams had more than twice as many unforced errors (11) as winners (five) and had made zero net approaches after winning 26 of 32 points at the net against Simona Halep in Wednesday’s quarter-final win.

That might have been in mind when she came forward to win the opening point of the second set. But Pliskova rattled off three straight points and Williams was made to face a break point for a fourth straight service game. She’d save them both – the second with a 106mph ace out wide – for another hard-won hold but the pressure was mounting.

Meanwhile Pliskova, a lean 6ft 1in figure with lengthy arms, continued to coast through her service games with unnerving dispassion, crushing deep, penetrating groundstrokes into the corners and offering Williams no quarter. On the rare instances when she did fall behind on serve, Pliskova’s booming rainmaker bailed her out. She rallied from 15-30 in the fourth game to cap another hold with consecutive 108mph aces for 2-all.

Pliskova then broke Williams for 3-2, but Williams broke back at love – the lone break point the Czech faced all night – and they were back on level terms.

Any doubts that had surrounded Williams, who turns 35 this month, had centered on a persisting shoulder injury, but ultimately it was a left knee ailment which compromised the American in the championship rounds. Surely it didn’t help that Thursday’s semi-final started less than 22 hours after Williams’s three-set win over Halep, but she denied the notion that fatigue contributed to her downfall.

“We play every single week,” the 22-times grand slam champion said. “I have been in Toronto or Montreal or Cincinnati where I play Wednesday, Thursday, Friday, Saturday, Sunday. I mean, if I’m not used to playing this, and I really should think of something different. I’m not going to sit here and make an excuse, because that’s not me.

“I’m a professional player. Been playing for over 20 years. If I can’t turn around after 24 hours and play again then I shouldn’t be on tour.”

The players continued to trade holds as the second set pressed on, though the injury-hampered Williams was made to work harder in her service games. When Pliskova pounded a 109mph ace to hold for 6-all, a tiebreaker would settle matters.

Pliskova rattled off the first three points but fended off a fightback from Williams, who went up a mini-break with a forehand winner for 4-3. But Williams double-faulted to give it right back before Pliskova got the best of a 17-stroke exchange – the longest of the night – to move within two points of the finish line. Williams then went long on a forehand, followed by the fatal double fault – her 31st unforced error of the night – that spelled her doom.

Williams described her knee ailment as “serious” and said it came up “after the second or third round” but declined to share the diagnosis.

“I’d rather not say, actually,” she said. “I wasn’t able to move the way I wanted to move. When you’re injured you’re thinking of other things when you should be just playing and thinking of your shots. My mind was just a little bit everywhere. But it was what it was.”

Pliskova refused to let the talk of Williams’ injury remove the sheen from her career-best win.

“I don’t care,” she said. “You know, sometimes it is like this. Not even me. I’m sometimes not playing when I’m 100% ready and I don’t think others care. If someone is not ready and she doesn’t think she is ready, she should not go on the court. But after the match I would say it’s still her choice if she wants to play or if she is ready to play or not.

“I’m just happy with my win, and I’m not gonna think about something like this.”

Pliskova had entered the US Open on a crest of momentum after defeating the world No3, Garbiñe Muguruza, and the No2, Angelique Kerber, en route to the Cincinnati title. But the 24-year-old, who reached a career-high ranking of No7 last year, went into the fortnight as the lone player in the top 20 who had never made it to the quarter-finals of a major, prompting murmurs over her nerve on the sport’s biggest stages.

Then came Saturday’s breakthrough win over Venus Williams, which propelled Pliskova into the second week of a grand slam for the first time in 18 appearances.

“Right now America hates me because I’ve beat both sisters Williams, but right now I’m very happy,” she said.

Now she’s become the fourth player to defeat both Williams sisters in the same major tournament, joining Martina Hingis (2001 Australian Open), Justine Henin (2007 US Open) and Kim Clijsters (2009 US Open) – and enters her maiden grand slam final on an 11-match win streak that includes five victories over opponents ranked in the top 10, none bigger than Thursday night’s historic scalp.

An even bigger prize awaits should Pliskova win Saturday against Kerber, the No2 seed who prevailed in Thursday’s second semi-final and will inherit the No1 mantle from Williams when Monday’s rankings are released. And given her blistering form, Pliskova will step on court with confidence to burn.

“Definitely it was about those last two, three weeks what I have played here in States and I won good matches. It gave me a lot of confidence, and that’s what tennis is all about. If you believe in yourself you can beat anyone. Especially in girls’ tennis it’s not only about a game and tennis, but it’s more about the mental things sometimes.

“So I really believe now that I can beat a good players. All of the players, actually now.”

Meanwhile, Angelique Kerber hailed an “incredible” day after she celebrated her new number one ranking by beating Caroline Wozniacki to reach the US Open final.

Williams’ shock defeat less than 40 minutes before Kerber’s match in Arthur Ashe Stadium sealed the German’s place as world number one and she underlined her credentials against Wozniacki, winning 6-4, 6-3.

Kerber will now take on Williams’ conqueror, Pliskova, in Saturday’s showpiece match as she closes in on a second grand slam title.

After finishing last year ranked 10th in the world, nobody could have predicted Kerber would go through 2016 as a three-time grand slam finalist and rated the finest female player on the planet.

Her rise began in January with a maiden major triumph at the Australian Open, where she had to defend match point against Japan’s Misaki Doi in the first round, and could now end with another success in Flushing Meadows.

Kerber beat Williams in Melbourne before losing to her in the final at Wimbledon, but it is a new face in Pliskova she will be facing this weekend after the Czech’s stunning victory in New York.

“I was watching the match a little bit before I came here but I was trying to focus on this match, not the match before,” Kerber said.

“It’s just incredible. It’s a great day. I was trying to play and focus on this match because Caroline is a great player, always tough to play against.

“To be in the final means a lot and to be number one in the world sounds amazing.”

Kerber is the first German to make the US Open final since Steffi Graf beat Monica Seles here in 1996 and also the first from her country since Graf to become world number one.

(Guardian service)