In the 11th minute Claudio Terzi came close to scoring the opener but his far-post header was tipped away from the top corner.
Three minutes later it was indeed 1-0 as Angelo scored with a stretching header from an angle to the right of goal.
In the 33rd minute Siena went another step towards the vital three points when Damiano Zanon put through his own net from the edge of the six-yard box.
Just seven minutes into the second half Pescara pulled a goal back as Mervan Celik found the top corner from the centre of the box.
Then out of nowhere they were level as Romulo whipped a 59th minute free kick into the top corner.
Just as it looked as though the match would end in a draw that would not help either side, Siena won it with five minutes to play as Innocent Emeghara found the net after a swift counter-attack.