The Steelmen soon found their stride and Clarkson dragged a shot wide and the restored McCormack had a drive palmed away by Ma-Kalambay.
But Hibs swept up the park to break the deadlock through summer signing Donaldson, marking his home debut with a fine goal after starting in place of the injured Steven Fletcher.
Brian Kerr played the ball down the left touch-line and Donaldson brilliantly dummied Stephen Craigan before racing in on goal, cutting across Mark Reynolds and netting under Graeme Smith.
The opener only galvanised Motherwell, who were level after 17 minutes, when McCormack's in-swinging corner caught Ma-Kalambay flat-footed and Clarkson glanced home a header.
Well went ahead three minutes later, when McGarry's cross picked out the unmarked Lasley at the back post to volley home.
It was a night of frustration for Hibs manager John Collins
Hibs were all at sea defensively and Clarkson found the net only to be ruled offside from another McGarry centre.
But a third goal for Mark McGhee's attack-minded men was only delayed thanks to the brilliance of McCormack.
The former Rangers striker collected 25 yards from goal and remarkably angled a lob over the giant frame of Ma-Kalambay into the top left-hand corner.
Ma-Kalambay was again forced to deny Clarkson as Hibs' fans vented their frustration.
Hibs boss John Collins hauled off Lewis Stevenson and Dean Shiels at the interval, bringing on Filipe Morais and Merouane Zemmama.
The tide initially continued flowing towards Hibs' goal, but Well were increasingly relying on the break as the home side pinned them back.
Smith stood firm in the 50th minute when he palmed away Rob Jones' header and Morais then fired a powerful drive just over.
Antoine-Courier let fly into the sidenetting and Zemmama saw a strike drift just inches past.
Guillaume Beuzelin and Donaldson went close, but Porter neatly slotted in an 83rd-minute fourth goal to end realistic hopes of a fightback.
Antoine-Curier pulled one back two minutes later - his first goal for the club - from Morais' cross, but Hibs had already lost their grip on the CIS Cup.
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