The Lilywhites trailed 2-0 at half-time, having gone down to 10 men in the 38th minute when Andrew Hughes was sent-off for bringing down Rhian Brewster in the box.
But in a super second-half show, North End shrugged off their numerical disadvantage.
Alan Browne cut the deficit in the 71st minute and then in the 89th minute Emil Riis levelled the scores - just as he had done in the reverse fixture at Bramall Lane in September.
Lowe said: "I was pleased with the character, resilience and desire of the boys because at 2-0 at half-time it a tough scoreline.
"It's tough to go in 2-0 down and it is also a tough scoreline for the opposition believe it or not.
"We had 10 men and I just asked the lads to give it everything they had got, we changed one or two bodies, we changed a few things around.
"When we got the first goal back we thought we would get another couple of chances because Sheffield United wanted to go and kill the game off.
"They couldn't do that, they had some chances but we had blocks on the line and headers, interceptions. I always felt we would get the opportunity to go down the other end.
"It is that never-say-die attitude in terms of what we are trying to do and what we are trying to build.
"We were frustrated with their first goal, it should have been dealt with when the ball came out, we should know those zones where we need to be to clear it.
"The penalty was a bit of a kick in the teeth, it was a penalty and it was a foul but I was a bit disappointed in terms of the sending-off.
"I thought the two of them sort of had arms together and that was about it. What a fantastic reaction from the group in there.
"After the game I said to them they are a good set of lads, it is the first time I had seen something which has made me think these can be a special group because of what they have gone and done.
"I don't know if you have seen that before at Deepdale where they were 2-0 down and came out fighting with 10 men to get a draw which feels like a win.
"Give Sheffield United credit, they are a good footballing team who opened us up a few times. That is the first time that has happened to us, we can learn from that.
"The fans need to take a lot of credit for that because they drove them in, the loudness, the noise, the screaming and shouting."
Lowe had to take off Scott Sinclair when Hughes got the red card in order to send on Greg Cunningham to plug the gap in the back three.
He then made a second change at half-time, Joe Rafferty coming on for Brad Potts.
Lowe said: "You can't coach character but you have to install it, install belief and that never-say-die attitude. That is what I want from them.
"I had to take poor Scotty off after 37 minutes on his first start for me. That is football, we had to make changes.
"We took Brad Potts off at half-time, we spun a few things around and put Joe Rafferty because we felt we could get more edge up that end.
"We still tried to play a bit and knocked a few long balls in which sometimes has to happen. We changed shape and went to a back four which is not really what we want.
"You have to do what is best at the time, we felt if we got another striker on the pitch we could get a goal.
"We had to do what we thought best on the football pitch when we were down to 10 men."
Reflecting on the goals North End scored, Lowe added: "They were two fantastic goals, we got the ball up the pitch a different way but once it was up there, wow.
"What a ball from Ched Evans for Emil's goal and DJ's for Al's.
"We slipped down the side and when you get in those areas we have got good footballers to put the ball in the back of the net.
"Overall I'm pleased with the performance in a different way and pleased with the character to stay in the game."
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