Jonathan Mills scored two of the away sides four tries and Ryan Hall claimed 11 points from the boot to seal a memorable win.
Risca of Division Four East put in a terrific performance to stun Croesyceiliog of Division Three East 20-15 away from home, while the students of Cardiff University pulled off another upset, beating Fairwater 17-14.
Rhydyfelin were the big scorers of the day, running home six tries on their way to a 41-0 demolition of Cilfyndd.
Mike Huckeridge claimed a try as Treherbert of Division Two East overcame a late scare to edge out Brecon 14-12, and
Tonyrefail came out in top of the all-Division Four East clash, beating Pentyrch 27-17 in a thrilling contest.
Elsewhere Mountain Ash beat Nelson 26-6, and Blaina claimed an impressive away win as they beat Division Three East rivals Abertillery Blaenau Gwent 20-8.
Abercarn pulled off the shock of the round in the Swalec Bowl, the Division Five East side beat Abergavenny of Division Two East 21-17.
Tries from Nicky Lloyd and Matthew Johnson had put Abercarn 13-12 ahead at half-time before Jack Davies put the home side 20-12 ahead. A late try from Abergavenny set up a tense finish, but the home side bravely held on to ensure a famous win.
John Mayler scored two tries as Old Penarthians gained an impressive 20-0 victory away at Canton and Ross Howells also claimed a brace as Ferndale beat Rhigos 20-8, Luke Rees claimed the other try for the Bulldogs.
Dowlais were the big scorers of the day as they ran in six tries to beat St Albans 45-3.
Crumlin put in a great performance away from home to beat Cefn Coed 34-0, while Usk also won away from home, they beat Llanhilleth 10-17.
Rhiwbina won 19-14 away at Cardiff HSOB, and Pontyclun also claimed a narrow win, beating Bridgend Sports 15-9. In the remaining game in the Swalec Bowl, Abervan failed to field a side against Newtown.
