Resuming Day 3 on 390/8, Glamorgan already held a first innings lead of 101 over Northamptonshire after dismissing the visitors for 279 on Day 1 with 9 of the wickets shared between Timm Van Der Gugten, James Harris and Andy Gorvin.
Glamorgan's lead was extended by a further hundred on the third morning due to valuable runs from James Harris 40, Mason Crane 56 not out and Andy Gorvin 26, to put the home side in a strong position.
Northants fared much better second time around and closed the day on 236/4 with Ricardo Vasconcelos having contributed 99 and the fifth wicket pair of Luke Proctor and Lewis McManus remaining unbeaten on 55 and 19 respectively.
