Invasive species cause substantial adverse effects to native wildlife, and there is great interest in understanding what makes invasive species successful. The lizard Anolis sagrei is a successful invasive species along the Gulf Coast of the United States, where they have displaced the native A. carolinensis. We predicted that A. sagrei’s success is due to their ability to endure higher temperatures. In this study, we compared performance of the two species in different microclimates to see if A. sagrei has an advantage over A. carolinensis under high temperatures. To estimate performance, we applied a biophysical model to calculate field operative temperatures for every hour over the past 25 years of A. sagrei’s Gulf Coast invasion. From the model, we predicted the threat of overheating for each species in full sun and shade. Additionally, heat hardening data were incorporated into the overheating model to determine if plastic responses contributed to differences in overheating risk between species. Heat hardening provided a clear advantage to A. carolinensis in open microhabitats, decreasing their annual overheating hours by an average of 36%. In contrast, A. sagrei did not heat harden; prior heat exposure decreased their heat tolerance and increased their susceptibility to overheating. Shaded microhabitats were important for both species to avoid overheating, providing operative conditions that rarely exceeded their heat tolerance limits. Collectively, these results suggest that A. carolinensis is better able than A. sagrei to tolerate the extreme heat present in their shared environment. As annual temperatures continue to rise, A. sagrei will face a greater threat of lethal temperatures which could benefit A. carolinensis in habitat reclamation.