New York, New York - Iga Swiatek stayed on course for a second grand slam title of the season after battling past Jessica Pegula and into the semi-finals of the US Open.

The world number one and French Open champion is the only player left in either of the singles draws who has previously lifted a slam trophy, and she raised her level in a 6-3, 7-6 (7-4) victory over the US' Pegula.

Both athletes struggled to hold serve and Swiatek was twice broken serving for the match, but she came through the tie-break to set up a clash with Aryna Sabalenka on Thursday.

Swiatek has not found her best form yet this tournament, but it has still been good enough, with only one set dropped so far.

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Eighth seed Pegula has been a rare consistent performer in the top 10 this season. This was her third major quarter-final of the year, but she is yet to go further.

She made the first move in the opening set with a break for 3-2 but let Swiatek back in from 30-0 in the next game. The Polish player was ruthless, dropping just two more points in the set.

The second set was a story of constant swings in momentum, with Swiatek, who was unhappy to be given a time violation in the fifth game, breaking serve five times only to be pegged back each time.

Pegula was given a warning for smacking a ball into the stands in frustration after another break for 4-3, while Swiatek had the most fortunate of net cords to move 5-4 ahead.

The pair were dragging each other all around the vast expanses of Arthur Ashe in lengthy rallies, but it was Swiatek who was more often on the front foot. She finally made it across the finish line to close out the game.