After the record-breaking exploits of Aneurin Donald, the second day in Cardiff belonged to Glamorgan's bowlers as Derbyshire were dismissed for 177 and asked to follow on. They reached the close on 78 for 1, still trailing by 263.
Craig Meschede took three wickets, and Graham Wagg and Andrew Salter picked up two apiece, as Derbyshire conceded a 341-run deficit on first innings. Wagg then claimed another - Harvey Hosein, having been promoted to open after top-scoring with 27 not out - but Derbyshire made a stronger start to their second attempt.
Glamorgan had added a further 37 runs to their overnight score and were all out for 518, with Meschede undefeated on 60. Derbyshire seamer Will Davis, in only his fourth first-class game, returned career-best figures of 7 for 146.
Hamish Rutherford and Billy Godleman made a rapid start to the Derbyshire reply, striking nine boundaries in the first five overs, and had reached 52 for 0 in ten overs before losing 4 for 19 runs before lunch.
Rutherford nicked Meschede to the wicketkeeper and Chesney Hughes was bowled off his pads by the same bowler, before Salter's offspin deceived Godleman, who was trapped leg-before. The Derbyshire captain was clearly not in agreement with the decision, and kicked the ground in anger, before trudging off to the pavilion. In the final over before lunch, Meschede took his third wicket, when Wayne Madsen tamely chipped a catch to square leg as Derbyshire slipped to 71 for 4.
There was no respite from the Glamorgan bowlers, as Graham Wagg bowled an excellent spell, with the ball swinging under cloud cover. Wagg dismissed Neil Broom and Shiv Thakor, both edging through to Mark Wallace, and the Glamorgan wicketkeeper claimed his fourth victim of the innings when Matt Critchley skied a catch, attempting to pull David Lloyd to the boundary. There was little resistance, apart from Hosein, and Derbyshire were soon batting again after the tea interval.
Hosein opened the second innings instead of Godleman, who had returned to the team hotel after feeling unwell, and with Rutherford playing every ball on its merit. The openers put on 59 in 27 overs, before Hosein was caught down the leg side by Wallace for 26 from Owen Morgan's left-arm spin.