Sloane Stephens saw her hopes of defending her US Open title go up in smoke on Tuesday as Anastasija Sevastova progressed to the semi-finals on a red-hot day in New York.

Stephens struggled throughout in a match that saw just three of the 17 games played won from the end of the court in the full glare of the sunshine, losing 6-2 6-3.

Sevastova coped better with the challenging conditions to book her place in a maiden grand slam semi-final against the winner of the last-eight clash between Serena Williams and Karolina Pliskova.

The turning point in the first set came with the players tied at 1-1 and locked in an attritional battle for the third game in which Sevastova faced four break points.

At one stage stewards inadvertently opened the doors, allowing a stream of spectators to flow into the stadium, causing a pause in play and an unwelcome distraction for the players.

But Sevastova held her concentration and her serve before racing to break in the next.

Stephens' failure to take her chances became a worrying trend as she squandered a further three break points in the fifth game, and a second Sevastova break to love wrapped up the set.

Third seed Stephens was wilting in the heat on what is expected to be the hottest day of a scorching US Open but, after falling 2-0 down at the beginning of the second set, she finally showed some fight.

A powerful forehand emerged from the shaded end of the court as Stephens converted a break point for the first time in the match, followed by a determined roar.

But the change of ends that followed forced Stephens back into the sunshine and she looked unsettled once more, berating herself as Sevastova moved 4-1 up with a win to love.

Stephens got back on serve from the shade once more but was unable to force a third set, as another break from Sevastova left her serving for the match, which she put to bed at the third time of asking.

STATISTICAL BREAKDOWN
Sevastova [19] bt Stephens [3] 6-2 6-3

WINNERS/UNFORCED ERRORS
Sevastova – 18/28
Stephens – 13/28

ACES/DOUBLE FAULTS
Sevastova – 2/1
Stephens – 0/1

BREAK POINTS WON
Sevastova – 5/8
Stephens – 2/9

FIRST SERVE PERCENTAGE
Sevastova – 54
Stephens – 82

PERCENTAGE OF POINTS WON ON FIRST/SECOND SERVE
Sevastova – 57/59
Stephens – 53/11

TOTAL POINTS
Sevastova – 67
Stephens – 51