A dominant first half showing saw Ponty take a 14-0 lead into the interval and it was a gap too big for the Welsh All Blacks to overcome.
Chris Dicomidis began the scoring with a try which outside half Humberstone converted and then with Neath’s Gareth McCarthy in the sin bin, wing Matthew Nuthall went over with Humberstone again adding the extras.
He slotted a penalty early in the second half to increase the visitors lead but Neath staged a mini-revival with an Aaron Bramwell try, and a conversion and penalty from outside half Dai Langdon. But that was a close as the home side came as Humberstone sealed the victory with a penalty and late drop goal.
Cross Keys join Ponty in the semis after a 37-24 victory over Cardiff at Pandy Park.
Dean Gunter was in superb form for Keys notching up 22-points with a try, conversion and five penalties while there were also tries for Dan Hodge, Nathan Trowbridge and Kristian Baller.
Outside half Gareth Davies tried to keep Cardiff in the game but despite kicking a conversion and four penalties to add to five-pointers from Joe Griffin and Will Jones, the Blue and Blacks never kicked on in the second half.
Outside half Dorian Jones kicked 20 points as Division One East outfit Ebbw Vale put Swansea to the sword. He converted flanker Ronny Kynes try, slotted over five penalties and added a drop goal as the All Whites bowed out of the competition.
Flanker Andrew Gwynne crossed for the losers in the first half but the Steelmen were worthy winners.
Newbridge made it two One East sides in the last four after edging out UWIC 13-3 at the Welfare Ground.
Full back Ryan Lee went over in the first half after gathering his own kick and with Neil Burnett converting and slotting over two penalties there was no way back for the Students whose only reply was a Rhys Roberts penalty.
SWALEC Plate
Two sides from Division One North made it through to the semi-finals with Bethesda slamming Three East’s Pontypool United 34-6, while Nant Conwy were made to work a lot harder before defeating Two East outfit Builth Wells 18-13.
In fact Nant Conwy had to overturn an 8-10 half time deficit with full back Carwyn ap Myrddin making the difference with a try, conversion and two penalties.
Bethesda were only 7-6 ahead at the interval but they blew their Three East opponents apart in the second half with a further three tries. Matthew Parry crossed for one, converted all four and added a penalty for a haul of 16 points.
Two East leaders Ystrad Rhondda look Plate favourites after a convincing 36-10 win at Two West’s Cwmllynfell. Alex Webber was the star of the show with 26 points from three tries, four conversions and a penalty.
Penallta ruined Maesteg Quins hopes of a return visit to the Millennium Stadium after losing out in last year’s Bowl final. Tries from Andrew Jenkins and Gregg Haynes helped Penallta to an 18-8 win.
SWALEC Bowl
Glyncoch of Six Central provided a major shock by dispatching Four West’s Amman United 18-16. Full back Shaun Baggs was the home hero landing six penalties to take his side into the semis.
Talywain of Four East made the long trip north to meet Dolgellau and two Wayne Redman tries added to one from Adam Williams made the trip worthwhile as Talywain won 18-11.
New Tredegar booked their spot after winning 22-17 at Resolven while Grant Williams notched up 12 points to edge Tycroes to a 27-24 victory over visitors Caerleon.
