Ricketts got the goal after six minutes after heading an inch-perfect Danny Pugh left-foot, left-wing cross into the keeper's bottom right0hand corner of the net from 12 yards.
Lonergan made two saves from Danny Haynes and then the follow-up from Jon Walters.
Preston striker David Nugent was booked for kicking the ball away and Matthew Richards went off injured for Town and was replaced by Gavin Williams.
Lonergan saved from Gary Roberts and Nugent shot wide when he was sent clear and should have done better.
Haynes was booked for dissent and Dan Harding was yellow-carded for a foul on Franck Songo'o just before half-time.
Ricketts was replaced by Danny Dichio at the interval, before Nugent had another shot which the keeper dropped before it went out for a right-wing corner.
Substitute Williams was booked for a foul on Dichio and Liam Chilvers shot wide, then Haynes fired over and Fabian Wilnis replaced Harding.
Callum Davidson had a 15-yard left-foot shot which hit the inside of the keeper's left-hand post, before Davidson was booked for a foul on Roberts.
Owen Garvan replaced O'Callaghan and soon after Chris Sedgwick was booked for a foul on the substitute, before Songo'o was cautioned for a foul on Roberts.
Preston brought on Patrick Agyemang and Brett Ormerod for Sedgwick and Songo'o as time ran out, before Town manager Jim Magilton was ordered to the stands right at the death.