In tricky conditions created by a brisk wind in the Californian desert, Raducanu looked uncomfortable throughout.
The 2021 US Open champion made a host of errors to allow Uchijima, a tenacious opponent who adapted to the breeze quickly, to come out on top of the often scrappy rallies.
Raducanu faced break points in her opening six service games as a result of the pressure created by the mistakes caused by her lack of accuracy.
Five of those games ended in Raducanu losing serve as she trailed by a set and a break to the 52nd-ranked Uchijima.
The Briton cut a subdued figure after she could not convert any of three chances to break back for 3-3.
After Uchijima dug deep to hold, Raducanu did not win another point and trudged off court having lost for a sixth time in her nine matches this year.
