Timm van der Gugten struck a career-best score to extend play into day four against Gloucestershire.
He combined with Ruaidhri Smith (34) and Kieran Bull (30) to give Glamorgan a slender 18 run lead with one wicket remaining in their second innings going into the final day.
"I'd got a heads-up on how to play on that wicket from bowling so much, so myself and Kieran tried to stay out there as long as possible and it becomes easier the longer you're out there, so it was just swallowing your pride and batting time," said van der Gugten.
"It was good to take it into tomorrow and get a bit of a lead, hopefully myself and Hoges (Michael Hogan) can bat a bit longer, get a hundred lead, you never know.
"It's good to get a fifty, but we're still behind the game with a lot more to do. We don't mean to get low scores, we're trying as hard as we can but we're a young squad and hopefully the guys learn from their mistakes to take it into the next games."