First half tries from Richard Howson and Hugh Llewellyn put Cowbridge level with the visitors at 10-10 going into the break before a disciplined second half performance saw their higher ranked opponents fail to trouble the score sheet.
That left the way clear for Lakin to steal the glory with his two penalty strikes
Tredegar are loving the cup this season, making it 146 points and 22 in their opening two games, as they thrashed Cwmgwrach 56-0.
Their eight try triumph came on top of a club cup record 90-0 first round victory against Pontllanfraith. Greg Jones took his personal SWALEC Cup tally to 41 points, with a 21 point haul courtesy of a try and eight conversions.
Former Welsh sprinter Jamie Henthorn and flanker Chris James both notched two tries each for the Division Two East team, while the visitors grabbed two consolation scores.
Division Five East Talywain shocked Division Three South-East Nantymoel in a 27-5 triumph. Gareth Needs got two tries and Adam Williams racked up 12 points through a try, a penalty, and two conversions at Emlyn Park.
Aberavon Quins also pulled off an upset by beating Abergavenny 5-3. Adam Dawe ran in an early try for Aberavon and a stern defence limited their Division Two East opponents to just one penalty from Steven Long.
Monmouth, of Division Four East, piled further misery on struggling Seven Sisters, knocking their Division Three South-West visitors out of the cup with a 34-17 home win. Gareth Morgan claimed two tries, with Andrew Griffiths, Adam Seymour and David Bruce also went over to send Monmouth through.
Bedlinog ran in 11 tries against Llanidloes in a 71-0 win at The Rec. Centre Thomas Cox and Lee Harrison each claimed a hat-trick of tries while Richard East ran in two against to humiliate the Division One North opposition.
Abercwmboi also claimed victory against northern opposition with a 29-5 win against Mold. Darren Cutland was the hero for Abercwmboi with two tries.
Barry went close to pulling off a major upset against Ynysybwl, but were left broken hearted after a last minute try condemned them to a 17-22 defeat. Three divisions separate the two sides but it took a last gasp effort from Ynysybwl centre Ceri Cummings on his first game since returning to the club, to see the Division Two East side through to the next round.