Delighted Poyet said Johnson's passionate celebration for his first goal indicates how driven his midfielder has become about sustaining top form.
"He didn't score in the cup, then we switched things round, so it's character. I like it," said Poyet.
"You give him options, you try your best to put him in the right positions, but at the end of the day, it's the player.
"I think he's a terrific lad, and you can only imagine how difficult it is when you change teams.
"You come in for a reason from a top team and you want to make a difference, and for whatever reason it doesn't work.
"It's easy to criticise and it's natural, but for the person, the player, it's sad.
"So he was desperate to do something special, and what a day today."