Tries from David O'Donoghue, Conan Gleeson and Ken White and two conversions and a penalty by Bennett had Shannon 22-6 ahead at half time. Barry Keeshan kicked two penalties for Dolphin.
Two tries from Mia Cronin both converted by Keeshan and three penalties looked like giving Dolphin victory, but Bennett's three second half penalties proved decisive.
Garryowen will face Shannon in the semi final after their 20-5 away win over Cashel. James McInerney, Harry McNulty and Alex Wotton scored tries for the Light Blues and Jamie Gavin kicked a conversion and a penalty. Brian Silke replied with a try for Cashel.
In the ODM Cyril Fitzgerald Plate Sunday's Well recorded their first win of the season with a 14-10 home win over Richmond. Thomas O'Brien scored a try after eight minutes for Richmond and three minutes into the second half Pat McNamara put the visitors 10-0 ahead. The 'Well hit back with tries from Ross O'Mahony and David O'Connell and Shane O'Riordan converted both.
Penalties from Dermot Fitzgerald and Rory Collins and a drop goal from Dara O'Neill was not enough for Thomond who lost 16-9 away to Highfield.
Young Munster booked their semi final place with a 34-17 victory over U.L. Bohemian at Annacotty.
ODM Munster Senior Cup: Cashel 5, Garryowen 20;
Old Crescent 20, U.C.C. 27;
Shannon 31, Dolphin 29;
ODM Cyril Fitzgerald Plate: Bruff 17, Nenagh Ormond 20;
Highfield 16, Thomond 9;
Sunday's Well 14, Richmond 10;
U.L. Bohemian17, Young Munster 34;
ODM Munster Senior Cup Semi Finals (November 16th)
Shannon v Garryowen;
U.C.C. v Cork Constitution.
ODM Cyril Fitzgerald Plate Semi Finals (November 16th)
Sunday's Well v Nenagh Ormond;
Highfield v Young Munster.