However, a dropped serve at the start of the decider had the world No. 50 back on the rack in her first match since the 21-year-old was diagnosed with glandular fever last month.
Rain earlier in the week ensured she had an extra 24 hours to prepare for the task in hand, but she came up just short.
“I’m really disappointed,” Watson said.
Asked if it did not comprise gamesmanship, Watson refused to criticize her rival for taking a bathroom break after the second set.
“Girls do it all the time. It’s just the norm. Maybe she did need to go, but I should have been focused and ready for whatever,” Watson said.
This year marks the first time in six years that no British player has reached the second round in Paris.
However, it was a good day for France as Jo-Wilfried Tsonga survived a first-set scare to advance into the third round with a 7-6 (8/6), 6-4, 6-3 win against Finn Jarkko Nieminen.
The sixth-seeded Tsonga, the last French man to reach a Grand Slam final at the 2008 Australian Open final, next faces either French 25th seed Jeremy Chardy or Spain’s Robert Bautista Agut.
Tsonga saved a set point in the first-set tiebreak, but then turned up the power and never looked back on a chilly Court Philippe Chatrier.
He ended the contest on his first match point with a backhand passing shot after less than two hours.
“I was opportunistic, I made the most of my chances,” Tsonga said.
Later in the day, Gael Monfils, who eliminated Czech fifth seed Tomas Berdych in the first round, was to take on Latvia’s Ernests Gulbis.
Agnieszka Radwanska’s hopes of playing little sister Urszula for a place in the last 16 were dashed.
Australian teen Ashleigh Barty, at 17 the second-youngest player in the draw behind 16-year-old Croatian Donna Vekic, reached the second round with an impressive 7-5, 2-6, 6-1 win over Lucie Hradecka of the Czech Republic.
The teen from Ipswich, Queensland, secured her maiden Grand Slam main draw success with a win in 1 hour, 54 minutes, moving on to a meeting with Russian 12th seed Maria Kirilenko.
All that was missing were her parents, but they were soon on the telephone.
“Mum and Dad are back home, my phone’s been going a bit crazy, but I haven’t had time to look at it yet,” Barty said.