British number one Heather Watson suffered an opening-round defeat for the second tournament in succession as she was beaten 1-6 7-5 6-4 by world number 50 Ayumi Morita in Miami.
The 20-year-old, who lost to Irina-Camelia Begu in Indian Wells last time out, easily won the first set.
But Morita hit back to lead 5-4 and broke Watson again to take the second.
The Japanese completed victory when she converted a third match point to knock out a player ranked 11 places higher.
Despite reaching her current career-high ranking in February, Watson is yet to beat a player ranked higher than her this season.
Watson benefitted from the retirement of world number 27 Sorana Cirstea in her season-opening event in Auckland.
She was denied the chance to change that statistic as Ayumi advanced to play Belgian world number 30 Yanina Wickmayer in the next round.