Having followed on, the visitors resumed on 201 for seven and the hosts showed no signs of letting them off the hook on Sunday morning.
Mark Wallace (43) and Michael Hogan (37) hung around long enough to get Glamorgan to 277, leaving Worcestershire needing 51 to win. They were 20 for no loss when the teams took an early lunch, and within sight of their third Championship win of the season
Essex advanced to 305 for seven - three runs ahead of Leicestershire on first innings - thanks largely to a James Foster century.
Foster was 103 not out at lunch, with Graham Napier the only wicket to fall so far today at Grace Road.