A 2-1 win at Fir Park means Motherwell - already sure of European qualification - will go to Pittodrie on the final day within one point of second-placed hosts Aberdeen.
John Sutton's penalty and a Gary Warren own goal proved good enough on the night, although Inverness' Billy McKay hit the post in the last attack of the game.
And McCall, who lost several first-team players following last season's runners-up finish, said: "It's incredible. Twenty-one victories.
"I said at the beginning of the season Celtic would win it, Hearts unfortunately because of the problems they had would be bottom, and Aberdeen would be second.
"That's because they've got such a good management team and a good squad of players. For us to be that near them is beyond what we could have dreamt of, but that's credit to the squad.
"Tonight wasn't the prettiest but we got the job done and we got that little bit of luck at the end. I think we have merited that over the season.
"We have taken it to the last game, we are proud to be in Europe and the only downside is wee Craig Moore looks like he has tweaked his cartilage."
Inverness manager John Hughes felt his side deserved at least a point - and a penalty for a handball when Fraser Kerr blocked a cross.
He said: "The full-back stopped a cross like a goalkeeper, so for me that's a penalty.
"But we put enough into it, dominated the whole second half, had them right on the back foot, played with a little more hunger and desire.
"Everything I'm looking for from an Inverness team. We played with more purpose and pace in the second half. I felt we were the better team, especially in the second half, but goals win games and if we keep conceding like that, we'll not win many."