To her credit, Raducanu battled back impressively in the second set and forced a tie-break after finally settling into the match.
But Sierra ultimately completed a 6-0 7-6 victory as Raducanu's miserable afternoon came to an end.
Emma Raducanu fought back tears after crashing out of the French Open and admitted she is simply "trying my best each day" following another painful setback in her difficult comeback season.