Sofia Kenin knocked out of US Open fourth round after straight sets defeat to Elise Mertens

Sofia Kenin is out of the US Open after a fourth round defeat in straight sets to Elise Mertens.

The no.2 seed, the highest-ranked player remaining in the tournament, was tipped to reach the latter stages after her maiden Grand Slam triumph at the Australian Open in January.

But the 21-year-old struggled to find the consistency that has made her one of the toughest opponents on the WTA Tour and was largely the architect of her own downfall with 26 unforced errors.

That should not take anything away from the unflappable Mertens, who served superbly throughout the match.

The 16th seed took control of the match after landing a double break and never looked back, sealing the first 6-3 in half an hour of play on Arthur Ashe.

Kenin showed some signs of resistance in the second set before an error-strewn service, where she made three consecutive unforced errors, allowed Mertens to take a giant step towards the quarter-finals.

The Belgian, who had lost her two previous meetings against Kenin having been a set up, was determined not to let this one slip and kept her errors to a minimum.

Serving for the match at 5-3, the 25-year-old kept her cool as Kenin desperately searched for a way back and sealed victory in an hour and 17 minutes on court with an fitting 103mph ace.

Mertens, into the quarter-finals for a second consecutive year, will face Victoria Azarenka in the last eight after she defeated Karolina Muchova in three sets.