Northamptonshire 157 (Cobb 54, Rossington 50, Salter 3-5) and 163 for 4 (Newton 89*) trail Glamorgan 371 by 51 runs
Glamorgan moved into a commanding position in pursuit of their second LV= County Championship Division Two win of the season as they pressed home a dominant position against Northamptonshire.
In Cardiff, Northamptonshire, who were following on after being dismissed for 157 first time around, reached 163 for four at the close and still trailed by 51 runs.
The home side were frustrated for a period by the Northamptonshire third-wicket pair of Rob Newton and Rob Keogh, with Newton striking 14 boundaries in his 89 not out. But it was again Glamorgan's day.
The morning's play was washed out, making it 116 overs that have been lost over the first three days, before Northamptonshire lost their last five first-innings wickets for 78 runs and were all out 65 short of the follow-on target.
Josh Cobb and Adam Rossington steered their team away from total embarrassment with a partnership of 91 for the sixth wicket in 22.1 overs, with both batsmen scoring half-centuries.
Rossington was unfortunate to be dismissed when a straight drive from Cobb was deflected by the bowler Ruaidhri Smith on to the stumps at the non-striker's end, while Cobb was lbw to Andrew Salter.
Young offspinner Salter cleaned up the tail to finish with career-best figures of 3 for 5 in four overs, while Craig Meschede also recorded his best in Championship cricket. Apart from the sixth-wicket pair, it was a sub-standard batting performance from the visitors on a good pitch which encouraged positive stroke-play.
With a lead of 214, Jacques Rudolph had no hesitation in enforcing the follow-on, and with the first ball of the innings Graham Wagg produced a lifter that Stephen Peters edged to Mark Wallace.
When the same bowler induced Kyle Coetzer to play on, Northamptonshire were 15 for 2, but any thoughts Glamorgan might have had of forcing a three-day win were dispelled by the third-wicket pair.
Newton was the most aggressive of the two, and was particularly severe on Smith whom he struck for three successive boundaries in one over.
Newton reached his fifty from 92 balls with seven sweetly timed boundaries, mostly through the off side, but after they had put on 107, Keogh struck the ball to mid-on and had no chance of beating Michael Hogan's direct hit.
Seven runs later, Northamptonshire lost their fourth wicket when Colin Ingram, bowling his leg-breaks for the first time in championship cricket, dismissed Cobb who skied to mid-on.