England appeared to be on course for defeat after a lacklustre display until they stuck late on to seal a late win.
England never got out of first gear as they were out-thought and out-fought by Scotland, while they were far too indisciplined.
However, despite Jonny Wilkinson being woefully off-form with the boot once again, they snatched victory in the dying minutes through Ashton.
Wilkinson did land two penalties and a drop-goal but he was off-target with his first three efforts - but ultimately it didn't matter.
For Scotland, Chris Paterson and replacement fly-half Dan Parks landed six points apiece but it wasn't enough.
Scotland were forced into an early change of tactic when Ruaridh Jackson, charged with playing a running game, limped from the field to be replaced by Parks after less than five minutes.
And given the horrendous conditions in Auckland, the change benefited the Scots, who changed to a kicking game.
Parks almost made an immediate impact with his cross-field kick knocked on by Sean Lamont. However it was Paterson who got the first points on the board, with the full-back making no mistake with his penalty attempt.
And England's issue with indiscipline reared its ugly head as they gave away a series of penalties - particularly at the scrum.
A long-range from Parks extended Scotland's lead - and while Scotland were taking their chances England were guilty of wasting theirs.
Wilkinson saw three penalties fail to find their target to increase to the frustration running through the England team.
Parks almost made them pay with a drop-goal effort that fell short but Wilkinson finally found his range on 33 minutes to give England some relief.
However a knock on from James Haskell at the restart gave Scotland the territory and possession again and it took good cover tackles from Wilkinson and then Delon Armitage to stop Joe Ansbro.
Parks, though, had the final word of the half with a drop-goal to give Scotland the 9-3 lead.
Having lack urgency in the first half, England came out firing for the second half - with a big hit from Manu Tuilagi creating an opportunity for Armitage, who raced down the wing but was tackled in to touch five metres short.
England's scrum was suddenly beginning to function as Scotland would put under pressure in their own 22 but Wilkinson failed to take advantage as he saw a poor drop-goal effort go wide.
However Scotland really should have scored a try on 52 minutes. Simon Danielli chipped over and although Ben Foden managed to get his hand to the ball it spilt loose but Nick de Luca could only knock on with the tryline at his mercy.
Scotland make the most of their visit into the England 22, though, with Paterson slotting over a penalty.
Unperturbed Wilkinson cancelled out the penalty with a well-struck drop-goal with his right foot - and the deficit was down to three points with a kick from out wide.
Tom Croft had to be alert to prevent Richie Gray winning the race to Parks' cross-field kick while Wilkinson saw another long-range effort drop agonisingly short.
However England snatched the victory at the end as a superb catch and drive took them towards the line before Toby Flood's pass out wide found Ashton to apply the finish. Flood converted.
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