Five unseeded players are through to the quarter-finals at the US Open Junior Championships in New York, with tie-breaks playing a crucial role for both Switzerland's Sebastianna Scilipoti and Argentina's Solana Sierra.

Scilipoti needed two of them to get past unseeded Sofia Costoulas of Belgium, with the 18-year-old recognising just how close her 7-6(6) 7-6(5) victory was.

"It was only a few points," said Scilipoti, who will be playing in her first junior Grand Slam quarter-final on Thursday. "She missed a little more than me at the end and I took my chances."

Scilipoti was determined to make the best of her fourth and last appearance in a Grand Slam junior event.

"I don't put any limit on myself," said Scilipoti, who reached the third round at the 2021 junior championships at Roland Garros. "I just go game by game, set by set, match by match. I came ready, with all the workouts, all the fitness I did, and it has paid off."

Sierra needed to break back twice with No. 13 seed Matilda Mutavdzic of Great Britain serving for the match at 5-4 and 6-5 in the third set, but the 17-year-old managed to avoid facing a match point. Down 4-2 in the decisive third set tie-break, Sierra benefitted from a net-cord winner, then crushed a forehand to earn the first match point of the two-hour and 43-minute contest. Another big forehand forced an error from Mutavdzic, giving Sierra, 0-2 in her only previous junior slam appearances this summer, a 3-6 6-4 7-6(4) victory.

The third unseeded girl to reach the quarter-finals is Petra Marcinko of Croatia, who defeated Alexis Blokhina of the United States 7-5 6-1 and will face No. 6 seed Kristina Dmitruk of Belarus in Thursday's quarter-finals.

The unseeded boys in the quarter-finals are Pierre Bailly of Belgium and Petr Nesterov of Bulgaria. Bailly ended the run of American wild card Colton Smith with a 6-4 6-4 victory, while Nesterov took out qualifier Jakub Mensik of the Czech Republic 7-6(3) 6-4.

Top seed Juncheng Shang of China had, for the second consecutive day, a difficult first set, this time against fellow 16-year-old Daniel Merida Aguilar of Spain. The ITF's No. 1 junior again survived the challenge, coming from a break down twice in the first set of his 7-6(5) 6-4 victory.

The Wimbledon finalists are the two American boys remaining in the draw, with champion and No. 2 seed Samir Banerjee extending his junior slam-winning streak to eight matches with a 5-7 6-1 6-2 win over No. 15 seed Maks Kasnikowski of Poland.

Banerjee has received prime court assignments in his two matches at his home slam, playing on Grandstand on Tuesday and on Court 17 on Wednesday.

"It's pretty cool and I can't take it for granted," said the 17-year-old from New Jersey. "So many people would dream of playing on these courts and I'm being put on them. It's not a full stadium, but it's still cool playing on these big courts, playing good players."

Banerjee served for the first set, and had four set points, but he failed to convert, blaming himself for a loss of concentration.

"I was just playing some pretty sloppy points on the set points," Banerjee said. "I'd make a decision that wasn't great. Honestly, if I had gotten that set, it would have been a more straightforward match. I kind of went away in that set, so I had to reset after that, but I think I did a good job of resetting after blowing that opportunity."

Banerjee began to extend rallies as he sensed Kasnikowski was wearing down after the Polish 18-year-old was taken to third-set tie-break.

"I could see he was kind of getting tired in the heat, so I tried to keep the pressure on," Banerjee said. "I could see him bending down between points, maybe going for some shots he normally wouldn't, not running for some balls. I knew he played a long three-setter the round before, so I knew if I just kept him out there long enough, just kept making him play, it would help me in the end."

No. 6 seed Victor Lilov, who lost to Banerjee in the Wimbledon final, defeated No. 9 seed Mark Lajal of Estonia 6-2, 6-2.

The top two seeds in the girls' singles draw were pushed to the limit on Wednesday, with No. 2 seed Alexandra Eala of the Philippines saving a match point when No. 15 seed Michaela Laki served for the victory at 6-4 5-4. Eala crushed a backhand winner on a second serve and went on to claim a 4-6 7-5 6-4 win, setting up a quarter-final encounter with Scilipoti.

Top seed Victoria Jimenez Kasintseva dropped the first set to two-time Orange Bowl finalist Jana Kolodynska of Belarus, but found her form in time to post a 6-7(5) 6-3 6-4 victory.

Jimenez Kasintseva faces No. 7 seed Robin Montgomery of the United States, who defeated No. 9 seed Natalia Szabanin of Hungary 6-2 5-7 6-4, in the quarter-finals. The other American hope remaining in the girls draw is No. 12 seed Elvina Kalieva, who defeated No. 5 seed Linda Fruhvirtova of the Czech Republic 7-6(3) 6-4.