Gloucester remain on track for their third Challenge Cup victory, having won in 2006 and 2015 and also their second piece of silverware this season after winning the Premiership Rugby Cup in March, despite not having a season to remember in the Premiership.
The hosts got off to the perfect start with Hathaway – starting in place of experienced Argentine Santiago Carreras who has just had appendix surgery – collected a punt over the top from Chris Harris to dive over for the first try of the day.
Tomas Albornoz – on his 50th appearance for Benetton – pulled back some points with two penalties, to one from Adam Hastings, but Gloucester looked in control.
Hastings kicked a brilliant 50:22 after the Italians sloppily lost the ball in midfield to give the hosts an excellent attacking opportunity and, at the second time of trying from a line-out, Gloucester’s maul drove forward and over with Blake scoring the second try to stretch the lead to 15-6.
Yet the tide turned when Gloucester number eight Zach Mercer was sent to the bin, five minutes before the break for a deliberate trip and Benetton instantly capitalised.
Winger Onisi Ratave saw a try chalked off for an infringement in the build up before Smith ran over in the corner with the clock in the red zone to close the gap to four points.
The hosts came out firing and looked the stronger team for early parts of the second half, and while Hastings kicked a penalty, replacement hooker Lucchesi powered over from a maul.
But Hastings, who has seen another season ravaged by injury and will leave Gloucester at the end of the campaign to re-join Glasgow, darted between two defenders to score a crucial try at a pivotal point.
Clarke capped a sensational interception and sprint downfield with a dive under the posts to add Gloucester’s fourth try seconds later as the momentum firmly swung the way of the hosts as they made it 32-16.
Lucchesi pulled another try back, rolling over from a driving maul, but it was too little from Benetton who were unable to become the first Italian side to reach a European Cup final.
Caolan Englefield’s penalty created a bit more breathing space for Gloucester before Thorley added the extras in the final seconds, scooping up a loose ball to run over and delight the rocking Kingsholm crowd.
