Wales Under-21 winger Nuthall scored out wide in the 79th minute to break a 12-all deadlock, and Ponty will be kicking themselves after dominating large sections of an uninspiring match.
Defending champs Newport needed a late try to scrum-half Bryan Shelbourne to bag a 20-16 over Gwent rivals Pontypool, while Llandovery sneaked home by three points at Aberavon, ruining a great debut by Wizards fly-half Liam Gadd, who scored all of the home side's points. Opposite number Gareth Morgan kicked his fourth penalty goal in the dying stages to secure a 19-16 victory.
Bridgend recorded a hard-fought 30-20 win over Caerphilly at the Brewery Field, scoring four tries to two in a performance that will sound a few warning bells among the top teams in the division. Wingers Grant Epton and Richard Mustoe scored good tries in the opening half to give the home side a match-winning 18-6 lead at the break.
Carmarthen Quins hammered Ebbw Vale 45-3, with a try double to centre Emyr Jones, while Neath accounted for regional partners Swansea 28-7 at the Gnoll. Fullback Gareth Morris and prop Paul Jones - two players on the edge of Ospreys selection - both scored tries while young goal-kicker James Hook added 10 points with the boot. Newly promoted Llanharan realise they're in for a long, hard season after losing 20-41 at home to Newbridge in their first game in the top division.
Results: Aberavon 16 Llandovery 19, Bridgend 30 Caerphilly 20, Cardiff 19 Pontypridd 12, Carmarthen Quins 45 Ebbw Vale 3, Llanharan 20 Newbridge 41, Neath 28 Swansea 7, Newport 20 Pontypool 16.
Playing today: Bedwas v Llanelli (2.30pm kick-off).