The Royalists intercept the convoy

The Royalist authorities learned of the relief expedition with disturbing speed, suggesting that the Junta's plans were thoroughly compromised. Jacinto de Romarate led a flotilla from Montevideo to intercept it before the reinforcements could reach Paraguay. His force included the brigs Belén and Cisne, four smaller armed craft, and supply vessels. Intelligence and an established naval base allowed the Royalists to turn material superiority into an interception on a confined river route.