Guzan had been a star throughout Villa's run into the semifinals, but he endured a rough afternoon.
Croatian Nikola Kalinic, who had hit the woodwork twice at home in the first leg, scored the first two Blackburn goals, on rebounds after Guzan could only parry David Dunn's cross and Martin Olsson's header.
Left back Stephen Warnock snuck in and leveled the score on aggregate on the half hour, but the game turned in the 38th minute when referee Martin Atkinson awarded Villa a penalty and dismissed Christopher Samba for a foul on Gabriel Agbonlahor.
James Milner put Villa back ahead from the penalty spot and it added three straight goals in the second half to pull away.
Jan. 20 in Birmingham
Aston Villa 6 Blackburn 4. Goals: Warnock 30, Milner (pen.) 40, own goal 53, Agbonlahor 57, Heskey 62, A.Young 90; Kalinic 10, 26, Olsson 63, Emerton 84.
Aston Villa -- Guzan, Cuellar, Collins, Dunne, Warnock, A.Young, Milner, Petrov, Downing (Sidwell, 86), Heskey, Agbonlahor.
Blackburn -- Robinson, Chimbonda, Samba, Nelsen, Givet, N'Zonzi (Reid, 61), Dunn (McCarthy, 55), Emerton, Pedersen, Olsson, Kalinic (Di Santo, 72).
Referee: Martin Atkinson.