Chievo and Hellas Verona had to settle for a share of the spoils after an end-to-end Derby della Scala ended 2-2 at the Stadio Marcantonio Bentegodi.
Rolando Maran's side, who had kept seven clean sheets in their last 10 outings, took an early lead when Alberto Paloschi nodded home Sergio Pellisier's cushioned header across goal from just a yard out.
Verona then completed a first-half turnaround when Luca Toni flicked another Hallfredson set piece beyond the reach of Bizzarri for his 19th Serie A goal of the season.
The game swung again before half time when Chievo were awarded a penalty after Hallfredsson sent Pellisier tumbling in the box, with the veteran striker picking himself up to tuck the spot kick into the bottom corner off the post.
Remarkably, Verona almost wrestled the lead back instantly as Toni hammered Bosko Jankovic's cutback off the underside of the bar.
The second half began with the same drama that characterised the first as Chievo were denied a penalty of their own within five minutes of the restart when Jankovic's handball was missed by the match officials.
Cristiano Biraghi then sent a curling free kick inches over the top of the bar as Chievo came to dominate possession, but they could not carve out the type of chances that they had in the opening 45 minutes.