Sandow kicked the lead out to 24 points in the 53rd minute before a Radradra mistake on tackle one allowed Matt Wright to dive over in the 57th.
From there the Cowboys ran in 24 unanswered points in quick succession, the first 12 of which came from Cooper pouncing on two similar Johnathan Thurston dinks into the in-goal.
The Cowboys second-rower nabbed his third when Will Hopoate spilled a Thurston bomb, and then he helped complete the comeback when he broke through the line and found a supporting Lachlan Coote, who kicked ahead for Kane Linnett in the 68th.
The Eels had burst out of the blocks with a try in the third minute, shifting the ball inside their own territory before Corey Norman eventually crossed under the posts.
More up tempo play allowed Norman to earn his team a penalty goal six minutes later, and then three charging Radradra carries and two offloads in one set ended in Takairangi going over in the 31st.
The visitors got one against the run of play when Michael Morgan jinked through some soft defence however the Eels replied shortly after when Manu Ma'u cannoned over the tryline.
Another Radradra try on the stroke of halftime kicked the lead out to 24-6.
Thurston said it was the best comeback win of his career and paid tribute to his left-edge second-rower Cooper.
"I can't remember chasing down that type of margin," he said.
"But Gavin Cooper was outstanding on our left edge, both in attack and in 'D', just punching through the line there.
"I can't remember scoring that amount of tries in that kind of space of minutes. We need to be better in some areas, but going into the bye with a win is how you want to be."
Eels coach Brad Arthur conceded the Eels have a major problem with mentally staying in games for 80 minutes and accused players of checking out at certain stages of the match.
"We drop our heads, we hear the footsteps coming and we just can't wrestle it back," he said.
"When you only play 70 minutes, you're not going to win. We've got to learn to play for 80 minutes.
Hooker Nathan Peats described the loss succinctly.
"To score four tries off kicks is pretty pathetic if you ask me," he said.
- AAP