It's a 30 limit both ways...
Tonmawr led 27-20 until a late try from Cardiff full-back Jimmy Norris set up a thrilling climax.
Fly-half Gareth Davies, who scored 20 points, converted to tie the scores and in injury time, he traded penalties with opposite number Luke Richards.
Ospreys wing Kristian Phillips got a debut try to send Ton into a 13-8 lead, but Cardiff led 14-13 at the break.
Tries from full-back Warren Davies and wing Kiba Richards gave Ton the edge, but Cardiff rallied to gain a second consecutive draw.
Tonmawr: Tries - K Phillips, W Davies, K Richards; cons - L Richards (3); pens - L Richards (3) Cardiff: Tries - M John, J Norris; con - G Davies; pens - G Davies (6)