Solar wind streams strongly influence planetary atmospheres as they propagate through the interplanetary medium. When these high-speed plasma flows reach Mars, the absence of a global dipole magnetic field prevents effective deflection of the solar wind, causing the flow to slow and form a bow shock. This, in turn, produces a compressed region known as the magnetosheath, where ions and electrons accumulate and solar wind density increases sharply. Although Mars lacks an intrinsic global magnetic field, it hosts strong crustal magnetic fields—primarily concentrated in the southern hemisphere between longitudes ~140°–240°—that further shape its plasma environment. These localized magnetic anomalies intensify magnetic field strengths during solar wind disturbances, enhance particle confinement, and lead to elevated electron densities above crustal regions. In this study, we investigate the response of Mars’ upper atmosphere to a strong solar wind event by combining in-situ measurements from MAVEN’s SWEA, MAG, and LPW instruments with heliospheric plasma simulations from EUHFORIA. This integrated observational–modeling approach enables us to track the solar wind disturbance from its heliospheric origin to its interaction with Mars, quantify variations in solar wind density, and examine magnetic field changes in both crustal and non-crustal areas. Our results reveal clear differences between these regions, demonstrating the crucial role of crustal magnetic fields in modulating the interaction between the solar wind and the Martian ionosphere. Understanding this coupling is essential for constraining atmospheric escape processes and for evaluating the long-term evolution of Mars’ atmosphere. More broadly, these results enhance our understanding of solar wind interactions at other weakly magnetized planetary bodies.