Fiorentina made a positive start as they hosted Como in the top flight for the first time since 1989, coming close to an opener through Robin Gosens’ close-range strike.
La Viola enjoyed a period of dominance thereafter, but it was the visitors who almost snatched the lead after 21 minutes when Maxence Caqueret picked out Diao, who forced David de Gea into a near-post stop.
The visitors continued to grow into the contest, with Diao very clearly the danger man, denied only by a last-ditch challenge from Marin Pongracic to prevent a shot in the box.
However, four minutes from half-time, Diao made his mark in a swift breakaway, finishing off a blistering run with a composed finish beyond the wrong-footed De Gea.
The hosts’ winning streak over Como was in jeopardy, having come out on top in their previous four meetings, each without conceding.
Searching for fresh impetus after the restart, Raffaele Palladino turned to his bench for a double alteration 10 minutes into the second half, yet clear-cut chances weren’t forthcoming.
In fact, things got even worse for the pre-match favourites as they soon found themselves two goals down, being punished for some loose play in midfield which led to a neat touch and fierce strike in off the post from Nico Paz - his first goal on the road this season.
With time ticking away, Fiorentina needed a response, but a tame Michael Folorunsho header was the best they could muster as Como saw out three valuable points.
A first clean sheet away from home in the league is a welcome sight for Cesc Fabregas, who sees his side edge away from the drop zone, now five points clear in 13th.
Meanwhile, back-to-back defeats for Palladino’s men put somewhat of a dampener on Fiorentina’s campaign, leaving them sixth.
La Viola stay inside the European qualifications spot for the time being, albeit having played one more game than AC Milan and Bologna, who each trail by a point.