REACTION: Warne "pretty chuffed" after last gasp Pompey win
The promotion hopefuls looked like they were set to share the spoils but Mattock rose highest at the back post to nod in home debutant Michael Smith's cross with just minutes remaining, to win 1-0.
And Warne was pleased with the performance, particularly in the second half.
He said: "You'll be pleased to know I'm pretty chuffed.
"The way the lads started the second half was excellent and they just kept knocking on the door.
"If we'd have come off with a 0-0 I would have still been proud of their performance.
"We were the only team trying to win the game but it didn't look like it was going to be.
"I've said to the lads how I proud I was of how they played and how they kept going."