Naomi Osaka fell to defeat against Danielle Collins in her opening match at the Abu Dhabi Open.
The four-time grand slam champion made her comeback last month following the birth of her first child, reaching the second round of the Brisbane International before losing a close contest to Caroline Garcia in her opening match at the Australian Open.
Those performances gave plenty of cause for encouragement but Osaka faded badly against American Collins, losing 7-5 6-0.
Rallies were few and far between in a first set dominated by serve until Collins claimed the crucial break at 5-5.
From there, the former Australian Open finalist ran away with the contest, with Osaka committing 20 unforced errors and looking dispirited as she dropped serve four times in a row.
Osaka plans to play a fuller schedule than she did prior to her 15-month break but it is clear the 26-year-old has plenty of work to do if she is to get back to the top of the game.
Collins, who is planning to retire at the end of the season, moves on to a second-round clash with top seed Elena Rybakina.