Andrew Hughes was shown a straight red card for a foul on Blades striker Rhian Brewster in the box.
It meant a reorganisation of the team by Lowe, with the shape of the team changing again as the second half unfolded.
Despite being a man down, North End battled back from being 2-0 behind to draw 2-2, Emil Riis scoring an 89th minute equaliser.
"Arsenal went down to 10 men early doors and it was that which went through my mind.
"As Hughesy went off I thought 'Here we go, five at the back, three in midfield and one striker'.
"But we were so disjointed in that shape, DJ and Alan Browne were so eager to get up the pitch. I was screaming at them to stay where they were.
"We kept it that way until half-time then I put Joe Rafferty on for Brad Potts and had Tom Barkhuizen to the right,.
"Tom had done a job for us on the left side because Sheffield United had big threats in Bogle and Basham down that side. I wanted him to help us out that way by pushing them back.
"That went out of the window when we had a man sent off."
The introduction of Ched Evans from the bench was key in the second half.
Lowe said: "We went to a 4-3-2, that messed them up a little bit and we were on the front foot.
"The full-backs were getting balls down the side and in behind, and we managed to score a great goal to get the equaliser."
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