United's first competitive action of the 2016/17 season saw them fall behind early on, hit back to lead at the interval and secure maximum points with a winner in stoppage time.
Nettleham included three players with much experience of playing at a higher level. Two of these combined for the game's opening goal which came with just under 75 seconds on the clock when Holly Newman broke clear from a cluster of defenders to head home a corner by Katie Davison.
United levelled through Jen Pearson with a strike from the right of the area midway through the half. Pearson scored her second when she converted a cross from the right on 38 minutes. With United having also been denied twice by the woodwork, they went into the interval 2-1 up and deserving of the advantage.
But it was a case of deja vu when play resumed with Nettleham again scoring early in the half, though this time taking a little bit longer before finding the back of the net, Abbie Murrell with a low angled shot a few seconds into the 48th minute.
Kirsty Johnson did well to turn aside a shot by Daisy Marsh to prevent the visitors regaining the advantage.
Kim Brown restored United's advantage from inside the right corner of the penalty area when a corner was only partially cleared,
United had a let off when Murrell's low shot beat Johnson only to strike the base of the left post but Nettleham levelled again when Courtney Limb scored from distance after a corner had not been fully cleared.
United, though, provided the final twist in proceedings with Brown latching on to a through ball and getting inside the area and from a similar position to where she had struck her first, chipped the ball beyond the reach of the goalkeeper Kirkham in the second minute of time added on.
Blades: Johnson, Cawthorn, Hopkinson, Ruddach, Neary, Spurr, Smith, Bell, Marsden, Pearson, Brown.
Subs: Darbyshire, Hickerman, Hall, Wainwright.