The British number two withdrew against American Madison Brengle in China after complaining of dizziness.
British number one Johanna Konta comfortably reached round two after beating German Annika Beck 6-1 6-2.
Ninth seed Konta will play China's Zhang Shuai in the second round.
Konta needs a strong result in the tournament to pass American Madison Keys and Spain's Carla Suarez Navarro in the race to qualify for the WTA Finals later this month, which features the season's top-eight players.
Guernsey-born Watson, 24, was suffering from a stomach bug when trailing her opponent 3-6 1-2 in mid-30C temperatures before pulling out on Monday.
"It came on this morning. I woke up in full sweats. I went out there to see how I feel but it wasn't great," said Watson, who also named John-Laffnie de Jager as her new coach on Monday. Watson has been without a mentor since splitting with Diego Veronelli earlier this year.
