Britons Kyle Edmund, Dan Evans and Heather Watson lost to qualifiers in the Miami Open first round, while Aljaz Bedene retired in his match.
Edmund was ahead before losing 2-6 7-6 (7-4) 6-2 to American Jared Donaldson.
World number 43 Evans was given a point penalty for swearing midway through the final set of his 7-5 0-6 6-3 loss to American qualifier Ernesto Escobedo.
Watson, who reached the fourth round last year, was beaten 7-6 (7-4) 6-1 by Romania's Patricia Maria Tig.
The defeat means the Briton will drop from her current world ranking of 108.