Jayne Ludlow's goal in the second minute of stoppage time at the end of extra time gave Arsenal a 2-1 win over Charlton.
Leeds earned themselves their first ever FA Cup appearance in a game they could have won by a bigger margin, having hit the woodwork no more than 3 times.
A 15-yard drive by Smith gave them a 23rd-minute lead which would have been extended by half-time had Nicole Emmanuel not hit the bar and Smith the post.
Northern Division side Liverpool battled throughout the second half but had the woodwork to thank again when former England winger Karen Burke tried her luck.
Burke then played a part in the killer goal, linking well with her one-time international colleague Karen Walker to set up Smith's second just before the hour.