The Socceroos skipper scored the only goal of Villa's play-off semi-final 1-0 aggregate win over Middlesbrough to qualify for the decider.

The Villans will face Fulham in the play-off final from 2am AEST on Sunday.

"It was important to keep calm after the semi-final win," Johnstone said. "All the lads were happy, of course. 

"But Mile Jedinak stood up, addressed the lads and said 'We’ve done nothing yet – let’s make this count in the Final'."

Johnstone went on to praise the 33-year-old Australian midfielder, who has been a key figure for Villa despite being in and out of the team this season.

"He’s been fantastic for us all season," Johnstone said.

"But we’ve had a great squad who have all played their part in getting us to Wembley. 

"We’ve had players coming in and out of the team, some playing out of position for the good of the team.

"The whole squad has been used and everyone has done well. That’s why we are where we are.

"But on Saturday and Tuesday, Mile was massive, simple as that – and he got the goal that got us through ultimately."