A great strike from Greg Tansey just before the interval gave Inverness the lead, and substitute Aaron Doran put the seal on the victory late on to give the scoreline a truer reflection of the visitors' dominance of the match
It was Inverness who started the brighter at a drenched Fir Park, passing the ball at pace on the slick surface.
They were getting into promising positions down both flanks, and forced two corners in quick succession, Ross Draper heading the second of these just wide.
Motherwell were almost gifted the lead however after quarter of an hour, Inverness captain Graeme Shinnie selling goalkeeper Dean Brill short with a pass-back meaning he could only find the feet of Lionel Ainsworth with a scuffed clearance.
The winger's attempted lob looked net-bound all the way only for Gary Warren to get back in the nick of time to clear off the line with his head.
Inverness were soon back in the ascendency though, and should have gone ahead after 20 minutes.
Tansey brought out a save from Dan Twardzik with a good effort from 25 yards, but the Motherwell 'keeper could only push the ball wide where Marley Watkins picked it up. His whipped cross found Billy McKay unmarked at the front post, but as the visiting fans stood to acclaim the opening goal, the normally deadly frontman skewed his effort wide.
Again Inverness came at the Steelmen, and only a fantastic block by young home-debutant David Ferguson prevented Ryan Christie from slotting home after a ball across the face of goal from Watkins.
John Hughes's men finally got the goal their dominance deserved after 42 minutes.
Tansey picked the ball up in midfield and drifted forward unchallenged before picking his spot with a great finish into Twardzik's bottom right-hand corner to give the Highlanders the half-time lead.
Stuart McCall reacted to his side's poor showing by replacing the ineffectual Ainsworth with Henrik Ojamaa at the break, making his first appearance since his midweek loan move from Legia Warsaw, much to the delight of the home fans.
They were almost stunned back into silence though as Inverness were the first to threaten in the second period, Shinnie advancing from his left-back berth to curl a right-foot effort just past the post from the edge of the area.
Inverness were continuing to look more comfortable in possession, and apart from one break by Stuart Carswell down the right when the midfielder did well to flash a ball across goal, Motherwell never seriously looked like threatening their advantage in the opening 20 minutes of the half.
Time and time again Motherwell were careless in possession, and even allowing for the numerous injuries that the home side were suffering from, it was a disjointed and sloppy display to that point.
Inverness were happy to keep possession for long periods in defence and midfield, with Motherwell's players struggling to get close to their opponents to exert any pressure.
There was little goalmouth action to speak of, but that suited the visitors who were content enough to sit on their lead.
When they did break out they looked dangerous however, and they got the second goal that their dominance deserved after 89 minutes.
Substitute Doran raced down the left before cutting inside and bending a beautiful right-foot finish beyond Twardzik, the final score not flattering the visitors who had outplayed last year's runners-up for the vast majority of the game.