Worcestershire 455 for 8 and 98 for 2 lead Glamorgan 374 (Root 118, Carlson 79, Leach 4-67) trail by 179 runs
Centurion Billy Root was the inspiration behind a stirring Glamorgan fightback after Worcestershire captain Joe Leach had plunged them into deep trouble with an early burst with the ball in the Bob Willis Trophy encounter at Blackfinch New Road.
Root, unbeaten on 53 overnight, had seen his side nosedive from 185 for 2 to 203 for 6 after Leach's spell brought the remarkable figures of 7-5-3-4.
At that juncture, the visitors were still 53 runs away from avoiding the possibility of being asked to follow on. But Root showed great application and determination in enabling his side to recover to the extent that their first-innings deficit was only 81 as they totalled 374 all out from 116.3 overs.
He went onto make 118 and it needed a stunning catch from Worcestershire keeper Ben Cox to bring his fine knock, containing 12 fours and spanning 258 balls, to an end.
Worcestershire openers Daryl Mitchell (48 not out) and Jake Libby (44) then extended their side's advantage in solid fashion during an opening stand of 97 before the latter and Leach (0) departed shortly before the close.
Root had received excellent support from Graham Wagg (54) in a seventh wicket partnership of 118 in 34 overs. The former Nottinghamshire batsman gave only one sharp chance when on 74 - to slip off spinner Brett D'Oliveira.
Then a last wicket stand of 41 between Timm van der Gugten (23 not out) and Michael Hogan (17) further helped Glamorgan's cause before they were dismissed on the stroke of tea.
Leach's initial spell wreaked havoc to the Glamorgan batting line-up. Kiran Carlson added only three runs to his overnight 76 when he pushed forward to a delivery which left him and Daryl Mitchell held a sharp low catch at second slip.
It ended a partnership of 141 in 47 overs with Root, and Leach struck again in his next over when Glamorgan captain Chris Cooke (0) went for a square drive and picked out Ed Barnard who excelled in clinging onto a low chance at point
Tom Cullen (1) was next to perish to a ball which moved away just enough to find the edge as he pushed forward - and Mitchell made no mistake with a chest high catch.
It became 203 for 6 with the last ball of the same over as Dan Douthwaite hooked at Leach and succumbed to a tumbling catch by Brett D'Oliveira running in from the mid-wicket boundary.
Only when Wagg joined Root did some much needed solidity return to the batting. A square cut for four off Leach - his 12th boundary - took Root to three figures from 258 balls.
Wagg's half century came up soon afterwards from 79 deliveries with seven fours before Root's spectacular dismissal. He nicked a delivery from Charlie Morris and saw Cox take a stunning one-handed catch in mid air away to his left.
The same combination accounted for Kieran Butt (7) in more straightforward fashion and then Wagg (54) top edged Ed Barnard to provide a simple catch to the keeper.
Dillon Pennington finally received some tangible reward to end the innings when Hogan was pouched by Barnard in another fine catch at point, as Leach finished with 4 for 67 from 26 overs, Barnard 3 for 54 and Morris 2 for 86.
Mitchell and first-innings century-maker Libby were initially watchful against some accurate Glamorgan new ball bowling from Hogan and van der Gugten.
But they gradually flourished with the 50 partnership coming up in 23 overs after successive boundaries by Libby off van der Gugten on his return to the attack.
Libby also hit Douthwaite for a trio of boundaries in one over but fell to the same bowler - caught behind - shortly before the close. Leach promoted himself but the move backfired when he was caught at slip by Charlie Hemphrey off spinner Kieran Bull.
