Essex resumed at 100-7 but added just 29 runs in 12 overs as Toole made the early breakthrough by bowling Zaman Akhter.
Simon Harmer played positively, but Sam Cook was caught at slip off Ul Hassan, and Harmer was last out for 35 when ul Hassan rattled his stumps to complete his five-wicket tally.
Essex looked likely to reach lunch without further damage, but ul Hassan changed that by bowling Paul Walter for 15.
The afternoon session was a completely different affair as Essex put their first innings nightmare behind them with Elgar and Westley looking largely untroubled.
Glamorgan worked their way through seven bowlers and a myriad of field changes without creating any chances as the visitors reached 169-1 at tea.
The stand had reached 166 by the time Westley was trapped leg-before by off-spinner Kellaway after batting doggedly for more than three hours.
Then Elgar went in Kellaway’s next over after hitting 15 fours, earning handshakes from the Glamorgan fielders and a healthy round of applause from the crowd.
Charlie Allison and Matt Critchley counter-attacked strongly to add 55 together, each hitting a six, but leg-spinner Mason Crane had Critchley lbw for 20 and then saw Allison (42) mishit a full-toss to mid-on.
Loanee wicketkeeper Bell, with half-centuries in both his previous matches, raced to a third off just 42 deliveries as he smashed Toole for four consecutive boundaries on the way to 59 not out.
Essex were within sight of making Glamorgan bat again, but face a new ball when play is possible on the last day.
Glamorgan’s Zain ul Hassan told BBC Sport Wales:
“It’s a big achievement and a dream of mine to get a five-for in first-class cricket and hopefully the first of many to come. I’m getting the rewards of the hard work I’ve been doing all season and I’m grateful I’m getting them now.
“I’m trying to be as accurate as possible and keeping those front-foot defence numbers as high as possible.
“Once the ball gets soft at the 30-over mark it gets a lot easier (to bat). In that first innings we’d already done most of the damage inside those 30 overs, but we’ve got a new ball now, so hopefully a few early wickets and go from there.
“We’ll try to get those wickets as early as possible, hopefully the rain does stay away and we’ll try to get whatever we have to chase.
“We haven’t really tried to do anything different in the last couple of weeks, but it would be good to finish with two wins on the bounce.”
Essex batter Dean Elgar said:
“We knew we’d be under the pump following on and hopefully the weather gods save us in a way, but today was a good effort from everyone, the fightback was a must, otherwise we’d be on the bus to Chelmsford tonight.
“I always want to perform even up to the last one, I always set the standard in regards to going out there and doing well. It didn’t happen first dig but I knew it needed someone like me and Tom to play a senior role, it’s nice to show you can do it even when the end is there.
“The boys were saying I write my own scripts which is not the case, otherwise I would’ve changed things but it’s nice to go out in good form.
“I’ve got to address the team tomorrow and the emotions will come when I go back to South Africa. I’m going to stay as far away from cricket as I possibly can (when I retire). I’ve been on the road 21 years and it takes a toll now and I just want to do something for myself.”
