Captain Chris Cooke was full of praise for batsman Kiran Carlson after he recorded twin centuries in the match - becoming the first Welshman to do so in the County Championship since 2005.
Carlson (129*) put on an unbeaten 107-run partnership with Callum Taylor (33*) for the 6th wicket to give Glamorgan a 62 run lead against Sussex heading into the final day.
"I think it was a pretty good day for us," said Cooke. "Kiran played unbelievably well and given us a bit of hope for tomorrow so we just need to keep fighting.
"I think it is just having a good positive game plan which Kiran has done all game and all season so far, looking to score and be positive. It can be quite difficult to score at times, but you have just got to stick in and you will get rewards.
"He has played beautifully, and he deserves all the accolades, he has worked really hard this winter. He batted three for us last year and he got a few good balls but he has come back really strong and he is looking the real deal now."