Batter Eddie Byrom struck a first-class career-best 176 to help Glamorgan pile up 494 against Sussex on the third day of their LV= County Championship match at Sophia Gardens.
Byrom and Colin Ingram set a new Glamorgan second-wicket record of 328 with Ingram top-scoring with 178 - his highest first-class score for the Welsh county.
With the lead 118 runs, Sussex reached 89/3 at the close, still 29 runs behind, with Ingram taking a wicket off the final ball of the day.
“That partnership with Colin was pretty special, a record-breaking breaking partnership so I was very pleased to be involved in that and I had my dad here to watch yesterday.
"It was pretty tough because I haven't played too much cricket recently, so mentally and physically tough, but the physios and strength & conditioning staff have done a great job when I was injured, to allow me to do that.
"There's not an awful lot in the pitch, but there is a bit of spin on offer and the odd one keeping low, so the surface is probably breaking up a little bit. Hopefully we can stick to our guns and chase not too high a score.
"(Clark's dismissal) was a very strange wicket, a yorker from Colin that rolled back onto his stumps so a great pole at the end of the day, and hopefully we can get one or two early tomorrow."