Longford caused a surprise by beating the reigning All-Ireland U-21 champions Dublin on a 1-06 to 1-05 in the Leinster quarter-final at Parnell Park.
Robbie Smyth scored the crucial goal for the winners on 53 minutes in a game played in wet conditions. The midlanders had Pádraig McCormack sent off near the end and had to withstand a Dublin onslaught that saw Ciarán Kilkenny narrowly miss a injury-time free to level matters.
Longford will next meet Wexford in the provincial semi-final after the Model County defeated Westmeath 2-10 to 0-15 after extra time.
Kildare ran out 2-15 to 1-09 winners over Meath in Navan, while Laois crushed Wicklow on a 6-11 to 2-08 scoreline in Portlaoise.