[1]: 58 On 11 July, 2,500 Paraguayans under the command of general José E. Díaz, attacked the positions outside the main Argentine camp perimeter.

The attack was stopped by dusk due to a grass fire set by the Congreve rockets, but soon resumed.

The Argentines lost 30 men killed, 177 wounded and 51 missing[1]: 59 López had dug two trenches during the night of 13 July, from which he planned on having snipers and artillery fire into the Brazilian left flank.

The Paraguayans were led by colonel Elizardo Aquino who was mortally wounded after 16 hours of fighting and four counter-attacks.

The Paraguayans suffered 2,000 casualties in the loss of the southern trench, while the Brazilians had 282 men killed, 1,579 wounded and 38 missing, and the Argentines lost 3 killed and 52 wounded[1]: 60 The Brazilians attacked again on 18 July, the flanking movement by general José Luís Mena Barreto and a frontal assault by general Vitorino José Carneiro Monteiro.