Yorkshire need three wickets against Glamorgan to win on the last day and stay in the lead to join Sussex, who have already been promoted.
After finishing the day 141 for 7, 254 behind, Ben Coad, the opening bowler for Yorkshire, claimed his 50th wicket of the year with a 4 for 30 total.
After dismissing Yorkshire for 273, James Harris claimed his 600th first-class wicket while finishing at 5 for 73 for Glamorgan. Asa Tribe, a Jersey international, was the lone hitter from Glamorgan to maintain his unbroken first-class half-century.
With the way wickets have fallen in each morning session of this match, Yorkshire will be sure of winning, even though that still set an unlikely goal of 396 for Glamorgan to win.
Jamie Harris and Andy Gorvin were determined to seize the opportunity when the morning conditions again favoured the bowlers. Harris got Finlay Bean leg before wicket in the first over, and Gorvin bowled nightwatcher Matthew Fisher clean with an off cutter.
Based on the idea that if a batter missed, he may either hit or file an appeal for leg before wicket, Harris dismissed James Wharton and Jonny Bairstow using the latter method.
Timm van der Gugten joined in the action, clean bowling George Hill, before captain Jonathan Tattersall and Dom Bess worked together to calm tensions.
After both reached their forties and the margin grew to almost 400, Ben Morris trapped Tattersall leg before wicket to give the Abergavenny rookie his first-ever first-class wicket.
Jordan Thompson was bowled or pinned in front by van der Gugten, marking the ninth wicket in a row that was removed by this method. However, they eventually obtained a different kind of dismissal when keeper Chris Cooke caught Bess, again from van der Gugten.
After taking out Dan Moriarty, Harris came back to finish with five wickets, including one clean bowled.
With the loss of their two leading run scorers for the season, Sam Northeast and Colin Ingram, their mountain of a 396-run deficit to overcome increased after the first overs.
In the opening over of their reply, Northeast was bowled out by Ben Coad for a leg before wicket. Ingram then proceeded to bowl in a generally good manner, chipping one to midwicket, where Coad again claimed the wicket and James Wharton made the catch. This was Coad’s 50th wicket of the year.
After hitting a golden duck in the first innings, Kiran Carlson would have wanted to get back into form for Sunday’s One Day Cup final at Trent Bridge against Somerset.
As he held the innings together, Tribe, who is playing in his second first-class match, easily recorded his greatest score. Carlson left for 41, but Coad’s superb leg cutter that struck the top of off made the difference.
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Ben Kellaway and Cooke followed him, both falling to Coad, and Matthew Fisher bowled van der Gugten. Finlay Bean’s incredible one-handed diving catch ended Mason Crane’s run against Jordan Thompson’s bowling.