United had won just two of their last eight league matches without the Spaniard in their starting line-up due to injury.
But Hernandez returned with a bang, setting up goals for Kemar Roofe and Liam Cooper during an inspired display, as Leeds returned to the top of the Championship.
“He was very important in the game,” Bielsa said.
“He played as if he was not injured previously. He was very intelligent with his game.”
Bielsa felt Leeds were full value for the three points after improving in the second half.
“It was a necessary win, a deserved one too,” he said.
“Our team was constantly offensive and we had 10 clear chances to score a goal.
“In the second half we defended well. In the first half it was hard for us to get over the way the opponent played the game.”
Leeds’ victory was soured by an injury to defender Gaetano Berardi in the first half.
“I think it is a muscular injury,” Bielsa added.
“He fell in an uncoordinated way and provoked an important tension of the muscle, meaning he couldn’t finish the game.”