The Blues sensationally battled back with two stoppage-time goals to grab a thrilling 4-3 win at the Keepmoat Stadium on Saturday.
The victory keeps alive their faint survival hopes going into tomorrow’s meeting with Crystal Palace at Fratton Park.
Pompey were pitiful in the first half against Dean Saunders’ men, falling two goals behind after just five minutes of the crucial game.
That prompted a reshuffle with Appleton withdrawing Kelvin Etuhu after 28 minutes for Kitson.
It had the desired effect with the former Reading striker a key man in Pompey’s stirring comeback.
Appleton heaped praise on the centre-forward, who looked to be finished at Fratton Park after being left out of the squad in recent games.
He said: ‘I have to give a bit of a special mention to Dave Kitson.
‘He’s taken a bit of stick from some quarters – and taken a bit of stick off me, to be fair.
‘I said to the players before the game there had not been a big enough impact from our substitutes.
‘But he was the catalyst for us and everything that happened.
‘He’s created one of the penalties, scored himself and made a big impact.
‘To be fair to him, Kits was key to everything we did well.
‘I wanted him to be aggressive but to do it within the rules.
‘I wanted him to show aggression and application without getting sent off. I wanted him to show a willingness to fight and give his all for the team – and he did that.
‘I think a lot of other players grew strength from that.’
What Appleton saw from certain players on Saturday underlined his belief that his squad needs a complete overhaul this summer.
Luke Varney was also hauled off at half-time with local youngster Ashley Harris thrown on.
The Purbrook teenager took his chance with both hands as he produced a fearless display.
Harris produced just the kind of hungry performance Appleton is looking for.
He said: ‘I have to give credit to young Ash as well. I thought he was quite intelligent when he came on. He played on that right-hand side and he made some clever runs.
‘He made some clever passing triangles with Joel Ward and one or two others.
‘He deserved an opportunity.
‘There were certain players in the first half who didn’t warrant the opportunity of going out in the second half.
‘What I did know I would get from Ash was an honesty, work-rate and application.
‘He would give that work ethic regardless of whether he got on the ball and things came off for him.
‘He gave us that.’