They had met six times before and Agnieszska Radwanska had won five of them, while CoCo Vandeweghe had come away with a total of just 28 games.
“Aga is a really difficult player to play against,” said Vandeweghe, who charted 49 winners to 54 unforced errors.
“She puts you in a lot of tough situations. You can second-guess yourself sometimes. I just tried to stay focused and regroup.”
Every set could have ended differently, to be honest. Sometimes you just need a little bit more luck out there, and I didn’t have that. She returned great, as she always does, so I knew to expect that, but the serve wasn’t there in the important moments. Agnieszka Radwanska
In their third round match at the US Open on Saturday, they played a classic and CoCo found her way past Radwanska in just four minutes short of three hours.
Vandeweghe started nervously and quickly found herself 0-3 down but she found her legs, and her length, and went the distance, outlasting the 10th seed, 7-5 4-6 6-4, to advance to the fourth round at the US Open for the first time.
It was an electric encounter, full of emotion and frustration from the American, in stark contrast to the calm disposition of her wily opponent.
The up-and-down first set saw no less than four service breaks.
It was Radwanska who drew first blood, jumping out to a 3-0 advantage with an early break, but the recently married Pole would double fault at 3-1, 30-40 to bring the set back on serve.
Vandeweghe squandered three set points serving at 5-4, tossing her racket to the Ashe Stadium cement in frustration, but eventually closed out the 64-minute set on a Radwanska error.
Vandewghe, whose address may well be in California but her heart and history are still in New York, where she was born, delighted her home fans by taking the first set.
The Pole battled back in the middle stanza, biding her time and scoring a set-sealing break with Vandeweghe serving at 4-5.
The two again exchanged service breaks in the third set before a pumped up Vandweghe, not one to conceal her emotions, pulled away for good, a forehand winner on her second break point of the seventh game the winning margin.
Serving for the match at 5-4, she struck her third and fourth aces of the afternoon, saving her best tennis for last.
She navigated a tricky final set to up-end her longtime nemesis, former World No 2 Radwanska and cemented her best-ever season after surging into the semi-finals of the Australian Open and the quarter-finals at Wimbledon.
After working with new coach and Hall of Famer Pat Cash, Vandeweghe has employed a hyper-aggressive game plan of late, making 49 forays to the net to get past the Pole in front of an enraptured crowd.
The deciding set featured five breaks of serve, but the American won a dramatic eighth game to put her four points from victory, serving it out behind 49 winners to 54 unforced errors.
A delighted Vandeweghe told the crowd: “There’s no better sound than you guys cheering me on.
“I’m doing my best out here. Aga is a difficult player to play. I have try to stay focused, go back to my routines, and play the next point… I only had one win against her; now I have two!”
A disappointed Radwanska maintained perspective in press, feeling the high-quality match came down to a few points.
“Every set could have ended differently, to be honest,” she said. “Sometimes you just need a little bit more luck out there, and I didn’t have that.
“She returned great, as she always does, so I knew to expect that, but the serve wasn’t there in the important moments.”
Standing between Vandeweghe and a first US Open quarter-final is Czech veteran and WTA Doubles No 1 Lucie Safarova, who ended the surprise run of Kurumi Nara in straight sets to start the day.
Brady struggles past Niculescu
Jennifer Brady reached the fourth round in her US Open debut, beating Monica Niculescu 6-3 4-6 7-6(3) on Saturday.
The 22-year-old American had never played a main-draw match at any Grand Slam tournament until January at the Australian Open, where she also made it to the fourth round.
Brady, who is from Pennsylvania, who is ranked 91, will face No 1 Karolina Pliskova for a quarter-final berth.
In the early going, it looked like the American might quickly overwhelm Romania’s Niculescu in their third-round match on Court 17.
Brady was making it look easy early on, rattling off five games in a row in less than 20 minutes in the first set as she hit booming shots from the baseline and easily handled Nicelscu’s persistent attempt at slice drop shots from both sides.
In the end, Brady would need to battle through a feisty effort from the Romanian, and she managed to eke out a close win to reach her first US Open fourth round.
The first set could have been closer as well.
Serving at 5-3, Brady showed poise as Niculescu tried to come in on a backhand slice and the American boomed a passing shot past her to take the set.
After that, Niculescu seemed more determined than ever to track down every ball and give Brady an even heavier heavy dose of the off-speed slice from both sides, which she used to great effect.
The two traded breaks early in the second set, and Brady broke again and held to go up 3-1.
A multiple deuce game at 3-2, with Brady serving, featured great shot-making from both players.
The game was punctuated by a Brady double fault to even the set.
The American struggled with her first serve throughout the match, landing just 58 percent on the day.
Niiculescu held at 3-3 after a lengthy game of grinding rallies and digging from both, as the Romanian came in off a forehand slice and volleyed a winner to take her first lead.
It was officially a dog fight.
The game at 4-5 was probably the longest and the hardest fought, as the two had a lengthy, multiple deuce game as Niculescu utilised a side-to-side drop shot routine.
Brady had her chances: on her first game point, she hit a big serve but netted the follow-up forehand.
Later in the game, Niculescu earned an unforced error over a winded Brady on the sixth deuce point and took the game and the set.
After about an hour and a half of up and down shot making, with both players sprinting side to side, the two headed to a decisive third set.
Brady immediately broke and then decisively held.
After that, both players struggled on their serves as the grinding match — with plenty of drop shot saves from Brady and side-to-side battles — was knotted in the third at 5-5.
A Brady hold put her up 6-5, giving the 22-year-old American another a chance to serve out the match.
Niculescu handled Brady’s serve well and the two went to a decisive tiebreak.
After Brady took a 4-0 lead, a couple of errors almost let the Romanian back into the tiebreak but the American was decisive.
An overhead smash winner put her up 5-2 but Niculescu, as always, came up with a reflex volley that was too deep for Brady.
A rare unforced error on Niculescu’s backhand gave Brady three match points at 6-3.
She took advantage of the first one: after a lengthy rally, Niculescu hit a backhand wide to give the American the match.
Svitolina sweeps past Rogers
American Shelby Rogers’ marathon run at the US Open has ended in the third round at the hands of Elina Svitolina.
Rogers, two days after winning the longest women’s singles match in US Open history, lost to the No 4-seed from the Ukraine, 6-4 7-5.
On match point, Svitolina hit a thunderous forehand that hit the net cord and dribbled over for a winner.
Svitolina, one of three players left in the women’s draw with a chance to leave Flushing Meadows at No 1, next faces the winner of the Saturday night match between No 15 seed Madison Keys and No 17 Elena Vesnina.
On Thursday, unseeded Rogers outlasted No 25-seeded Daria Gavrilova 7-6 (6) 4-6 7-6(5) in 3 hours and 33 minutes.