决胜 is a separable verb (离合词) meaning 'to decide the victory' or 'to clinch the outcome of a game or battle.' It is often used in competitive or strategic contexts (e.g., 决胜局 'deciding game', 决胜千里 'plan victory from afar'). As a separable verb, you can insert aspect markers like 了 or 过 between 决 and 胜: 决了胜 ('decided the victory'), 决过胜 ('have decided the victory'). The object it governs is the victory itself, so after splitting, what comes between is typically aspectual, not a separate object.