Both teams were looking to enhance their European aspirations and the game started brightly at the Caledonian Stadium with chances at either end.
Ryan Esson was forced to punch away Vigurs' inswinging free-kick, while Graeme Shinnie went close from 25 yards.
Greg Tansey then had an effort from similar distance for Caley as the visitors partially cleared a corner.
Motherwell opened the scoring after 39 minutes when Fraser Kerr's long ball split the home defence and Henri Anier ran clear before dispatching a low effort into the corner of the net via the post.
Well looked content to sit in and soak up the pressure at the beginning of the second half, although Vigurs showed the visiting team were still a threat with a floated free-kick that landed on the roof of the net.
Inverness needed something to provide a spark for them and only a fine block by Stephen McManus denied Greg Tansey as he pulled the trigger from James Vincent's incisive pass.
Tansey went closer moments later, firing one in from 30 yards that had Gunnar Nielsen beaten, but his effort hit the post before bouncing away to safety.
Frustration was beginning to set in for the home fans but substitute Ryan Christie brought Caley level with 16 minutes left to play.
The ball broke to the youngster and he hit it sweetly from 25 yards, beating Nielsen and finding the corner of the net.
But the hosts' European ambitions suffered a massive blow when Vigurs grabbed the winner eight minutes from time against the run of play.
Danny Devine was left isolated as Vigurs and Craig Moore worked several passes between them before Vigurs finished off a composed effort from just inside the 18-yard box.