The visitors plunged to 28 for four, with veteran seamer Matthew Hoggard claiming all four at a cost of just 12 runs in his first appearance since April.
But Mark Pettini, recalled to the side after last week's embarrassment, hit his first Championship half-century of the season to lead the recovery, and Essex closed on 196 for six in reply to Leicestershire's 302.
Worcestershire edged closer to their third Championship win of the season as Glamorgan continued to take a pounding at New Road.
At the start of the third day the home side needed 15 wickets for victory and by the close they had taken all but three of them with Glamorgan still 28 short of avoiding an innings defeat.
Jim Allenby propped up the Welshmen with 82 in their first-innings dismissal for 277 and weighed in with an unbeaten 53 when they batted again, trailing by 228.
- Sports & Recreation
- Matthew Hoggard
- Mark Pettini