The former Black Caps cricketer Jesse Ryder finished with a career best 10 wickets as Essex handed Glamorgan their first English County Championship defeat of the season with a 248-run win.
Set a huge 462 for victory, the Glamorgan began the day on 110-1 but lost seven wickets before lunch.
Ryder, who took four wickets for 53 runs in Glamorgan's second innings, and David Masters cleaned up the tail, as Glamorgan made 213.
Ryder took 6-47 in the first innings to finish with career best figures of 10 for 100 from the match.
Glamorgan's hopes of surviving the day, or even chasing down the remaining 352 runs, were dealt a blow in just the second over of the morning when captain Jacques Rudolph edged Ryder's outswinger behind.
Wickets continued to tumble but not before 18-year-old Aneurin Donald reached his second first-class half-century off 91 balls.
However, after Donald top-edged a catch to James Foster off Masters, the rest of the batting line-up folded as Glamorgan lost their last five wickets for 55 runs.
The Welsh county remain in third place in Division Two, 17 points behind Surrey and a promotion spot, while Essex move up to fourth.
The Essex batsman Nick Browne said, "We knew how important this game was, it was a must-win. Glamorgan have been playing some good cricket and are right up there themselves."
"They bat all the way down so we've done well to get them all out for 213, especially as the wicket got better as the game went on."
"Jesse's been fantastic this match and the bowlers have been magnificent all season."
"I don't like facing Jesse in the nets. He nips them both ways and he's quicker than people think."
The Glamorgan head coach Toby Radford also heaped praise on the former New Zealand international.
"It was disappointing the way we folded, especially as we still believed it was possible to win the game at the start of play."
"But full marks to Ryder. He got the ball to nip back both ways and always posed problems."
"On a positive note, I was delighted with the performance of (Aneurin) Donald. He's a young lad with a lot of talent and we feel he has a great future ahead of him."
"This was our first defeat of the season and we can be proud of the way we have played up until now."