Leeds Rhinos boss hails super subs after win at Salford Red Devils
Rhinos trailed 8-0, but gave themselves a lifeline with a try on the final play of the first half and went on to dominate the second.
The double introduction of Cuthbertson and Myler was pivotal.
Gale scored on the stroke of half-time and Jack Walker completed Rhinos' scoring late on.
"They gave us a real injection of energy, control, experience and from that point on we were probably the better side," Agar said of Myler and Cuthbertson.
"We had a lot more energy in the second half in the way we played and kicked the ball.
"It wasn't real pretty, but sometimes you have to roll your sleeves up and scrap a win, which we did."
Agar described it as a "game of two halves".
He said: "I thought we were really scrappy and poor in the first half.
"We didn't utilise the wind well enough and we came up with five or six errors coming out of our own end.
"The try just before half-time was critical, it gave us a spring in our step.
"In the second half we played with a bit more control, made less errors and took our chances when they came.
"It was pleasing to keep another opponent to two tries."