Left-back Threlfall latched on to a Torquay clearance in the 83rd minute to send a 20-yard drive back in over a packed penalty area and beyond the outstretched reach of goalkeeper Michael Poke off the underside of the crossbar to cancel out Aaron Downes' 17th-minute opener.
Bentley said: "The fans who travelled down here will have something to cheer them on the way home because that was something special, a wonder strike."
Downes had powered home a header from Damon Lathrope's corner from the left.
Lathrope was one of five players recalled to the Torquay starting XI by caretaker boss Geoff Harrop, the club's director of youth.
Another of those five recalled players, Elliot Benyon, saw his header come back off the crossbar while strike partner Karl Hawley also hit the post in a first half dominated by the hosts.
Bentley said: "It was a very tough afternoon and we knew it would be because they were up for it, despite not having a manager, because they have had a tough start to the season and find themselves in the bottom two.
"They had a caretaker manager in charge and a crowd favourite in Kevin Nicholson coming back into the side and a new player in loan signing Joss Labadie.
"The caretaker manager made a handful of changes and on paper it was a strong Torquay side and you could just sense when they warmed up they were all up for it.
"The pitch didn't play too badly in the end and credit to the referee for going ahead with it, because he made the decision after the second pitch inspection at 11.30. It was borderline, so it was great to get it on.
"Then the crowd got behind them and credit to Aaron Downes, he hunts the ball down and the goal he got, I said to him I would have been proud of that one myself, he attacked it well and powered it in.
"The four goals we have conceded in the last three games have all come from set-pieces and that's something we need to tighten up on.
"Thankfully we rolled our luck and they didn't take their chances when they hit us on the break in the second half and when you need something special, you get it from your left-back smashing it into the top corner.
"I thought it was a great goal for us and we didn't want a third defeat in a row."
Torquay caretaker-boss Harrop could not hide his disappointment.
He said: "I think all-in-all I don't think we have had a shot to save and I was really disappointed with the result because three points were there to be taken.
"The guys have set some great standards and I can't really ask anymore of them.
"On a really heavy pitch they have worked their socks off and I think the home supporters appreciated that.
"It was great to see the fans stay behind at the end to cheer the players off and you can see they are fully behind the players, which is really important.
"The fans were magnificent, they kept us going when we had some tired legs out there.
"I also thought the back four were magnificent because we had to stay strong.
"They kept to their jobs, it's just unfortunate that a wonder strike has dampened our spirits.
"But we come in again next week and the boys now know the standard that's required at this football club and if you want to be part of it then you have got to come up to scratch.
"As you could see from this performance they are fully behind what we are trying to do."