The candidate topological superconductor UTe2 exhibits a complex phase diagram with multiple superconducting states, yet the nature of their coexistence has remained a central mystery. In particular, the apparent intersection of two second-order phase boundaries at a “triple point” in the pressure-temperature phase diagram is thermodynamically forbidden, suggesting hidden phase transitions or a fundamental misunderstanding of the superconductivity in UTe2. We use pulse-echo ultrasound to resolve this puzzle by discovering a new phase boundary that is characterized by a unique “upward jump” in the sound velocity—direct thermodynamic evidence for a re-entrant phase transition. Our results establish (P⋆, T⋆) as a tetracritical point, beyond which the ambient and pressure-induced superconducting order parameters form a multi-component state. We use the measured phase diagram to construct a Ginzburg-Landau theory that shows that strong competition between the two superconducting order parameters drives the re-entrance and leads to phase locking that suppresses superconducting fluctuations. These findings provide the definitive magnetic field-temperature-pressure phase diagram and establish a thermodynamic foundation for multi-component—and potentially topological—superconductivity in UTe2.