Victor Genes' men led courtesy of Roque Santa Cruz's deflected strike late in the first half, before the hosting Peruvians had striker Paolo Guerrero sent off in the 67th minute.
But a stunning cameo from substitute Ascues saw the Peruvians steal victory in front of their home fans.
Ascues equalised when put through by Cristian Benavente moments after gracing the field in the 72nd minute, before the Universidad San Martin man struck the winner eight minutes later.
There was late drama, just as there was in the clash in Luque, with each of Peru's Yordy Reyna and Paraguay's Derlis Gonzalez - both substitutes - sent off in injury time.
Santa Cruz opened the scoring in the 42nd minute, his control of a high bouncing ball on the edge of the Peruvian area seeing him fire off a shot - which deflected off the back of defender Luis Advincula and past goalkeeper Pedro Gallese.
Substitute Ascues, though, had an immediate impact on the contest, netting twice in eight minutes to provide the answer to coach Pablo Bengoechea's attacking woes.
Juan Manuel Vargas also saw his left-foot effort denied by the left post in the 78th minute.
The Paraguayans had created the better chances in the first half, Paulo da Silva's volley in the fourth minute clearing the crossbar before Santa Cruz placed his header wide moments later.
Up the other end, Peru number nine Guerrero was the main man but he was unable to get an effective shot at goal until first-half injury time - when he narrowly pulled his long-range strike wide.
Instead, Guerrero's battle with Gustavo Gomez was the centre of attention - with the Peruvian front man gradually growing frustrated throughout the opening half and fortunate to stay on the park.
Guerrero stomped on Paraguayan defender Gomez, which only earned him a yellow card in the 31st minute.
His night would have been ended even earlier had powerhouse club Corinthians had their way, as Guerrero's inclusion ruled him out of a key domestic clash in Brazil.
Guerrero claimed he was elbowed in the face by Gomez earlier in the contest before his lash out after the half-hour mark, and was later tackled to the ground by Cristian Riveros - as the attention on the number nine intensified.
Guerrero's night eventually did end early, as he earned his second yellow of the match in the 67th minute for a deliberate handball foul.
Substitute Andre Carrillo went on a winding run in the 72nd minute, forcing a corner for his undermanned side - and after the corner was partially cleared, the ball fell for Ascues, who unleashed a brilliant shot that was just wide of the right post.
Ascues broke free moments later, dancing past defender Luis Cardozo before slotting into the bottom left corner past a stranded Justo Villar.
And the 22-year-old completed the stunning comeback by getting on the end of a sweeping Peru move that saw them move the ball from the left sideline in midfield to the attacker on the right, and he finished at Villar's near post.
