Evidence from sequential-task studies demonstrate that if the first task requires self-control, then performance on the second task is compromised (Hagger, Wood, Stiff, & Chatzisarantis, 2010). In a novel extension of previous sequential-task research, the first self-control task in the current study was a sport psychology intervention, paradoxically proposed to be associated with improved performance. Eighteen participants (9 males, 9 females; mean age = 21.6 years, SD = 1.6), none of whom had previously performed the experimental task or motor imagery, were randomly assigned to an imagery condition or a control condition. After the collection of pretest data, participants completed the same 5-week physical training program designed to enhance swimming tumble-turn performance. Results indicated that performance improved significantly among participants from both conditions with no significant intervention effect. Hence, in contrast to expected findings from application of the imagery literature, there was no additive effect after an intervention. We suggest practitioners should be cognisant of the potential effects of sequential tasks, and future research is needed to investigate this line of research.