Townsend's Gregor men appeared to be well on their way to a ninth consecutive Championship victory in this fixture as they racked up three tries in the opening half-hour en route to a 2210 lead.
Even when Italy, who had lost their last 26 home games in the Championship since 2013, reached the interval within six points, the game was still well within the Scots' command.
But the momentum shifted dramatically when what would have been a fourth Scotland try, for scrum-half George Horne, was ruled out for a clumsy obstruction by prop Pierre Schoeman early in the second half.
Within two minutes new Italy wing Louis Lynagh collected a chip over the top to dot down a debut try and suddenly belief flowed through Azzurri ranks.
In contrast, the technical and mental frailties. that have prevented Scotland from managing more than three wins in any Six Nations and becoming genuine contenders resurfaced once again.
They conceded a string of penalties - seven to Italy's one in the second half - and lost the clinical edge in attack that had served them so well in the opening period.
Scotland still have a Triple Crown to play for in Dublin on Saturday, but having not beaten Ireland in nine meetings under Townsend, it would be a brave man who bet on them breaking that streak.
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