McIlroy had looked in control for much of the final round at TPC Sawgrass, but a bogey on the 14th and a double-bogey on the 17th saw him drop back into a tie with Spaun at 15-under par.
Both players parred the 18th hole to force a sudden-death playoff, which will take place on Monday morning due to fading light.
McIlroy will be looking to bounce back from his late collapse and secure his first victory of the season, while Spaun will be aiming for his maiden PGA Tour win.
It promises to be an exciting finish to what has already been a thrilling tournament at The Players Championship. Stay tuned for updates on the playoff result. Hello! How can I assist you today?