All the goals goals came in the second half, with Gylfi Sigurdsson firing Reading in front shortly after the break only to see Brett Ormerod equalise just short of the hour mark.
There were seven minutes left when Rasiak, on for the injured Simon Church, fired in a right-foot effort to win the game for Reading.
Sigurdsson was in the right place to fire home Jobi McAnuff's left-wing cross for the opener, while Ormerod finished off a left-wing centre from Charlie Adam.
Reading could have won the game in the opening ten minutes, which saw Blackpool keeper Matt Gilks make a string of fine saves from a rampant Royals side.
In the first minute, Job McAnuff ended a run down the left with a centre which Wales international Church headed goalwards only to see Gilks fingertip it way for a corner.
Five minutes later, McAnuff tested Gilks again with a shot the keeper could only parry before it was cleared to safety.
Gilks continued to earn his wages with a comfortable save from Brian Howard's free-kick that was straight at him.
Then he made an instinctive save from Church's close-range effort following Sigurdsson's corner.
Gilks continued to defy Reading by saving a fierce Jimmy Kebe effort and the game was still only 12 minutes old.
It was one-way traffic and Sigurdsson shot wide before Kebe's cross was headed just wide by the industrious Church.
Against the run of play and with just four minutes of the first half remaining, Ben Burgess came closest of all to scoring.
With time to spare, he planted a firm left-foot shot against the upright and saw it bounce away to safety.
Eight minutes from the end, Burgess was close to scoring for Blackpool with an effort that curled just over the bar.
Then came Rasiak's winner.