Cresswell's first, which came after just 42 seconds set United on course for a win that never looked in doubt.
The three points will help them get their play-off push back on track after a run of three games without a win and extended their impressive unbeaten run at Bramall Lane to 11 matches.
By contrast, their form on the road has been woeful, having lost their last seven games, and with a trip to South Yorkshire rivals Doncaster on the horizon Speed is desperate for the Blades to transfer their home form to their travels.
"We need to get a result away from home," said Speed.
"It is obviously mental, the sooner we change that the better and the boys can take a lot of heart out of the result.
"Out of the 18 players that got changed tonight, only four were here at the start of the season. The credit has got to go to the players and the performance was fantastic."
Meanwhile, Speed has confirmed that on-loan goalkeeper Mark Bunn has been recalled by Blackburn.
Bunn, who has been at Bramall Lane all season, will return to Rovers to cover the absence of Paul Robinson and it leaves the Blades looking for a new stopper.
"Bunny has gone now. He has been recalled. We need to thank him for everything he has done. He has been fantastic," he said.
"I am sure we will be looking to bring someone in."
Blackpool boss Ian Holloway conceded that his side did not deserve anything out of the game.
"Conceding after 42 seconds wasn't part of the plan but after that I thought we got the ball and stayed composed - apart from the final third," he said.
"You have to say overall they did better in both boxes than we did."
Blackpool are slipping out of play-off contention and back-to-back defeats have left them in ninth position, five points behind the top six.
Holloway added: "The last two results haven't done us any favours whatsoever. We have got nine games left it can change again just as quickly."