Emily Murphy's sixth WSL2 goal of the season clawed the Lasses level before half time after Simone Sherwood had put the Blades ahead minutes earlier, but there were no further goals at Bramall Lane.
The visitors did have the ball in the back of the net through Emilia Larsson, but she was denied a first goal for the club when Murphy was adjudged to have committed a foul in the box just seconds before the Swede fired home.
"Frustrating," was how Oxtoby described the result in South Yorkshire. She said: "We weren't at our level at all in terms of energy and performance in the first half.
"I don't think we brought the energy levels to the game and didn't match the levels that they showed.
"We addressed that at half time in no uncertain terms and changed our shape so there was more accountability going player for player and get numbers higher up the pitch."
Murphy's well taken goal just before the break did little to dismiss Oxtoby's annoyance at her side's first-half display.
She said: "I think we need to be better, because we wasted 45 minutes of football, albeit scoring two and one being disallowed, but we still wasted 45 minutes in my opinion.
"I didn't think we were at it, and in this league you need to perform for 90 plus minutes, and that is a lesson learned tonight."
With two games to come this week for the Lasses, both at home, United's Australian manager sees no better way to put this result to bed and move on with the season.
"I think that's the beauty of our schedule at the moment," she added. "We're focused on Wednesday's game, after a disappointing result away from home.
"So we'll go back to Newcastle and get ourselves prepared for Birmingham."




