Some suit jackets work much better as sportscoats than do others. Without seeing the suit jacket in question, it's difficult to give a meaningful answer to your question.
I'm tempted to suggest that taking it that extra step from "sportscoat" to "blazer," should involve the changing out of the suit jacket's buttons with metallic ones, but I acknowledge that this may be nitpicking. Although replacing an orphaned suit jacket's buttons with ones that are more sportscoat-like (say, leather buttons), can help in transforming it into its new wardrobe role. It's not a particularly expensive or difficult change, and it can really make a major difference in the look and perceived level of formality of a former suit jacket.
But, again, some suit jackets can manage the transition pretty well, and others can't. Show me some pictures, if you want a more solid answer from me than that.