NEW YORK (AFP, REUTERS) - Second seed Sofia Kenin of the United States was sent crashing out of the US Open on Monday (Sept 8), beaten in straight sets by Elise Mertens of Belgium.

Kenin, the highest seeded player left in the tournament and winner of the 2020 Australian Open, was bundled out of the last 16 6-3, 6-3, in 1hr 14 min by Mertens.

Kenin, who had not lost a game in her first three rounds, never got her service game together against Mertens. The 21-year-old Moscow-born player won only 56 per cent of first-serve points compared to 75 per cent for Mertens.

Kenin also hit three double faults, while Mertens hit none. The Belgian, ranked 18th in the world, smashed eight aces, while Kenin failed to muster any.

Mertens, the 16th seed, will now play Victoria Azarenka of Belarus in the quarter-finals.

The revitalised Azarenka reached her first Grand Slam quarter-final in more than four years after rallying from a set down to beat Czech Karolina Muchova 5-7, 6-1, 6-4.

The 31-year-old twice Australian Open champion was broken three times in the opening set but 20th seed Muchova looked increasingly hampered by a problem with her upper left thigh on Louis Armstrong Stadium.

Azarenka, on a high after winning her first title for four years at the Western & Southern Open, took full advantage of Muchova's discomfort to whip through the second set and even the contest.

Muchova took a lengthy medical timeout and returned heavily strapped for the decider but unseeded former world No. 1 Azarenka would not be denied and marched on to a last eight date with Mertens.