McCarthy doubled his goal tally for the season against Motherwell
James McCarthy's brace consigned Motherwell to a fifth straight defeat and took Hamilton level on points with the Steelmen at the bottom of the SPL.
McCarthy slotted the ball past Graeme Smith from six yards with only injury time remaining of a poor first half.
Motherwell rallied in the second period only for Accies to double their lead after Mark Reynolds failed to clear.
And McCarthy was also on hand to clear John Sutton's header off the line as Motherwell pressed late in the game.
Motherwell's current league position is in stark contrast to the third-place finish that secured Uefa Cup football last season.
Only goal difference keeps them off the relegation spot, although they have now only scored once in their last seven matches.
With so much at stake, it was the visitors who looked eager to get forward in the very early stages, but it was Hamilton who passed up a good chance to go in front on five minutes thanks to striker Richard Offiong's heavy first touch.
Both teams struggled to create chances in a match full of energy but short on quality, with each side continually relinquishing possession easily.
With 25 minutes on the clock, Jamie Murphy stretched to head wide from Stevie Hammell's deep cross before Smith raced off his line at the other end to beat Offiong to James McArthur's deflected shot.
Tomas Cerny was forced to save from Paul Quinn's 25-yard drive, and then tip over Chris Porter's good turn and shot, as the match started to liven up after the half-hour mark.
However, almost immediately after those fine stops, the Czech goalkeeper was forced to retire from the match suffering from the effects of an earlier collision with Sutton.
Just as the match seemed to be heading to the break as a stalemate, McCarthy burst forward from midfield to slot Simon Mensing's through-ball under Smith to give Accies the lead.
Motherwell boss Mark McGhee must have given a rousing team talk at half-time as his men came out fired up for the second period.
In the first five minutes of the half, Sutton, Porter and Keith Lasley all threatened as the Steelmen laid siege to Sean Murdoch's goal.
As Accies defended their lead desperately, Mark McLaughlin was forced out of the game after taking a knock from his own goalkeeper.
But, rather than Motherwell clawing back a deserved equaliser, it was Accies who doubled their lead on 67 minutes.
McCarthy pursued a long ball over the visitors' defence, Reynolds failed to clear the danger and the Accies midfielder slipped the ball under Smith.
Motherwell were denied a spot kick when Sutton appeared to be tugged by David Elebert.
And, as the away team continued to press, Murdoch dived to pluck Porter's goal-bound header on the line.
In the closing stages, the goal-scorer was on hand to hack Sutton's header off the line to safety as Accies survived five minutes of injury time to claim an important three points.
Hamilton Accies manager Billy Reid: "We're over the moon at the club at the moment, to win against our rivals.
"It wasn't the best of games. It wasn't pretty to watch, but there have been times this season when we've been great and we've got nothing.
"Today we've crowned it - and young McCarthy, what more can you say about him? What a player. He deserved his goals."
"His progression the last couple of years has been staggering. He played here at 15 years old and then we knew we had something special.
"Now he's doing it at Premier League level and that's the highest level you can do it in Scotland."
Motherwell manager Mark McGhee:
"I wasn't ranting and raving in the dressing room after the match. But we've got to find out why we're not winning football matches.
"Even with the players missing we're still a lot better than we've shown today.
"I've got to keep them together and believing in each other.
"We're not playing as a team at the moment,
"There's a sort of virus going right through the team at the moment stopping us from playing as a team. We're more like disconnected individuals.
"But I'm convinced we'll get better and win football matches, and by April we'll be in a comfortable position."
E-mail this to a friend 
Printable version 
Bookmark with:
What are these?