Although Liverpool displayed a great deal of skill in the early stages, with El Hadji Diouf emerging as a major threat, it was Villa who created most of the danger.
They weathered some early pressure when Diouf gave Alpay, who made his first home appearance since last December, a hectic time.
Liverpool were indebted to goalkeeper Jerzy Dudek for keeping them in the game when he finger tipped a Steve Staunton header on to the bar. From the rebound Staunton, falling to the ground, hit the post with his second effort and again the ball bounced clear.
The only time Villa were in real trouble in the opening half occurred when Steven Gerrard broke down the right and his cross found Diouf running in from the left only for the Senegal striker to loft his effort over the bar.
Michael Owen made his first impression eight minutes before the break with a sudden surge but Peter Enckelman narrowed the angle to make a fine save to boost his own confidence after taking over as first choice from the departed Peter Schmeichel.
But Enckelman had little chance three minutes into the second half when a Danny Murphy pass found Riise, who was accorded a free shot on target as Mark Delaney lost his footing.
Riise scored with a low shot beating Enckelman at the near post as Villa's defence was guilty of some indifferent marking.
With Villa seeking an equaliser Liverpool staged a smart attack down the right and Gareth Barry fouled Gerrard only for Owen to blast his 79th minute penalty straight at Enckelman