Heather Watson has been knocked out of the Luxembourg Open at the quarter-final stage due to a straight-sets defeat to Elise Mertens.

The 21-year-old Belgian needed less than an hour-and-a-half to come back from a break down and claim a 6-4 6-4 win over her British opponent.

Watson was well beaten in the first set but improved in the second, only for two poor games in a row to put her behind for the first time, conceding a 5-4 deficit with a poorly-hit forehand as her serve collapsed.

The decisive game saw the 25-year-old continue to make errors and, despite a slight improvement, directed a forehand well wide to give Mertens the match.

Mertens will take on Monica Puig, who beat Watson's compatriot Naomi Broady, in the semi-finals.