Former Motherwell midfielder Simon Mensing headed the opener on the hour mark after Tomas Cerny had kept Accies level with a string of saves, including a penalty stop from Ross Forbes.
Motherwell sub Jamie Murphy scored a spectacular equaliser but the visitors needed a Lukas Jutkiewicz goal to earn them a point four minutes from time after Marco Paixao had headed Accies back in front.
Hamilton were a man down for most of the game after Guillaume Beuzelin received two bookings inside two minutes and Cerny was by far the busier goalkeeper.
Motherwell manager Jim Gannon had to make three changes following injuries to Shaun Hutchinson, John Ruddy and Yassin Moutaouakil.
Former Inverness goalkeeper Michael Fraser made his first SPL appearance for Well while Stephen Craigan returned and winger Chris Humphrey deputised at right-back.
Well created the first chance of a frantic opening when Jutkiewicz turned and shot at Cerny and John Sutton had the ball in the Hamilton net in the 12th minute when he attacked Humphrey's cross, but the striker took out Cerny in the process and referee Craig Thomson blew for a foul.
Hamilton enjoyed some decent possession in the opening quarter and James Wesolowski set up Beuzelin on the left side of the box but the Frenchman sliced wide.
The former Hibernian midfielder was booked after sliding in to bring down O'Brien and less than two minutes later tripped Reynolds as the left-back skipped past him.
There was no doubt both challenges were fouls but Accies boss Billy Reid was furious with the resultant red card.
Cerny scrambled Tom Hateley's free-kick wide but Hamilton almost caught Well on the break when Marco Paixao's pass gave Mickael Antoine-Curier a yard of space inside the box, however the striker sliced wide.
O'Brien earned Motherwell a 39th-minute penalty when he was brought down by Richard Hastings' clumsy tackle but Cerny parried Forbes' centrally-placed spot-kick.
Steven Saunders' header was cleared off the line from O'Brien's corner and Cerny made another flying save from Hateley's long-range effort in injury-time.
Gannon took off Craigan with Hateley dropping back and Murphy coming on at right wing and Cerny saved Hamilton again two minutes into the second half.
Good play from Sutton and O'Brien set up the overlapping Reynolds but his low drive was straight at the Hamilton keeper, who then blocked Sutton's follow-up.
Sutton headed just wide from O'Brien's corner and Giles Coke shot wide before Hamilton survived a two-on-one break when Martin Canning cut out Murphy's pass for Jutkiewicz on the edge of his box.
Paixao shot over from a 25-yard free-kick and Fraser had yet to make a save when he picked the ball out the net in the 60th minute as Mensing found space to head Paixao's corner into the far corner.
Motherwell almost went further behind when Saunders lost Antoine-Curier as the striker was found by McLaughlin's long ball, but the on-loan Dundee man shot inches wide of the far post.
Cerny pounced on the ball under pressure from Coke and Jennings shot wide from eight yards but Motherwell's pressure had subsided before Murphy scored a glorious 78th-minute equaliser. The Scotland Under-21 international made space for himself 30 yards out and curled into the top corner.
Jennings shot just wide from 20 yards but Hamilton incredibly regained the lead in the 81st minute when Paixao headed into the corner from 10 yards after Wesolowski broke down the right and crossed.
But Well levelled again in the 86th minute when Cerny could not keep out Jutkiewicz's sidefoot finish following Coke's low cross from the right.
Motherwell were also reduced to 10 men for the final stages after Humphrey pulled a hamstring and Cerny saved Accies again in injury-time when he diverted another Reynolds effort over the bar.