The much-changed Newcastle side went ahead through Danny Guthrie only to trail 3-1 in the early seconds of the second half to a couple of Theo Robinson goals and another from Jordan Rhodes.
Geremi pulled back a goal with his first strike for 18 months and then supersub Ameobi, on at the start of the second half, levelled it up from the penalty spot before heading the winner to take his season's tally to six.
Jose Enrique made an excellent break down the left after 16 minutes and got in a decent cross and Guthrie failed to make any contact when the slightest of touches would have meant a certain United goal.
Kevin Nolan, who scored the only goal in a 1-0 pre-season win at Huddersfield, had the ball in the net with a cool finish but his
celebrations were cut short by a raised offside flag.
A terrible pass from Anthony Pilkington proved crucial on 36 minutes. He passed the ball blind and only found Danny Guthrie who finished with some style to beat Alex Smithies.
But Huddersfield responded magnificently and within a minute it was all-square again when Tamas Kadar lost Theo Robinson who finished by slotting the ball through the legs of goalkeeper Tim Krul.
It then got worse for United when Krul brought down goalscorer Robinson after 29 minutes with the slightest of touches.
Robinson picked himself up and the 20-year-old striker struck the ball into the bottom right hand corner.
Chris Hughton responded to Newcastle's need for more striking power and Ameobi was introduced after the break in place of Nicky Butt.
But before Ameobi had a touch Huddersfield went 3-1 up in the 47th minute when Jordan Rhodes struck his sixth goal of the season after breaking on the right .
Krul needlessly committed himself well out of his goal and Rhodes coolly slotted in from the tightest of angles.
This time it was Newcastle who hit straight back within a minute with a great finish from Geremi to make it 3-2 for his first goal since scoring in a United win at Tottenham in March 2008.
The referee then evened up the penalty stakes after 62 minutes when Ameobi went down under pressure from Andy Butler in a tangle of legs and the big striker struck his second penalty of the season for his fifth of the campaign to make it 3-3.
Newcastle got the winner in the 83rd minute with a second from Ameobi. Guthrie's free-kick from the by-line was headed downwards by Ameobi and just to make sure Nolan pushed the ball into the net.