Background <p>Individuals with chronic primary cervical pain (CPCP) often exhibit cervical sensorimotor impairment. Although upper cervical spinal manipulation (UCSM) is commonly used, its immediate effects on sensorimotor control remain unclear. This study investigated the immediate effects of UCSM at the C1–C2 segment on cervical sensorimotor control in individuals with CPCP using the cervical movement sense (CMS) test.</p> Methods <p>This study was an exploratory, single-blind, sham-controlled randomized controlled trial with a blinded outcome assessor. Thirty-five individuals with CPCP were recruited between May and June 2024 and randomly assigned to an experimental group (EG, <i>n</i> = 18), which received UCSM, or a control group (CG, <i>n</i> = 17), which received sham manipulation. The primary outcome was movement accuracy (MA), and secondary outcomes included movement time (MT), movement speed (MS), and movement accuracy–time ratio (MAT). These variables were assessed before and immediately after the intervention using a customized algorithm for video analysis in the CMS test. Each kinematic variable was analyzed using a two-way mixed-design ANOVA.</p> Results <p>For MA, the Time × Group interaction was not statistically significant (<i>p</i> = 0.050). However, significant Time × Group interactions were observed for MT (<i>p</i> = 0.003) and MS (<i>p</i> = 0.001). Post-hoc analysis revealed that the EG showed a significant 11% decrease in MS (<i>p</i> = 0.002), whereas the CG showed a significant 13% decrease in MT (<i>p</i> = 0.009) and a significant 8% increase in MS (<i>p</i> = 0.042). No significant interaction was observed for the MAT (<i>p</i> = 0.055).</p> Conclusion <p>This exploratory trial suggests that UCSM may have elicited a transient slowing of head and neck movement in the CMS test compared with sham manipulation. Under the task instructions emphasizing accuracy, this slowing may reflect a movement pattern favoring accuracy over speed, aligning with the speed–accuracy trade-off. Considering the descriptive trend toward increased MA, these kinematic changes may also be compatible with compensatory sensorimotor control immediately after UCSM. However, given the exploratory nature of this study, these interpretations should be accepted with caution. Future research is needed to validate these exploratory findings in a larger sample and to determine their long-term clinical relevance.</p> Trial registration <p>This trial was retrospectively registered with the Clinical Research Information Service (CRIS), Republic of Korea (KCT00010683) on June 25, 2025.</p>