Target-man Ball converted a Jordan Chapell pass to open the scoring in the third minute and then doubled his tally in first-half stoppage time after Byron Harrison had levelled from a 12th minute free kick.
Ball's strike partner Karl Hawley made it 3-1 in the 49th minute and, although Terry Gornell went solo to make it 3-2 in the 65th minute, Ball teed up winger Chapell to cap the Gulls' victory at the death.
Knill said: "All week we have been working on getting Callum in the box and if he gets in the box we know he can finish. He did that today and it will be a massive boost to his confidence.
"I said to their coaching staff at half time that it could be four all. In the first half it looked like they could score but we could score - it was so open. At the same time, if you want to play expansive football and want to score goals, sometimes you have to risk that.
"I have got to say I am absolutely delighted with the players because they worked so hard for these three points and we just said in the changing room 'that's how hard you have to work every week if you want to be successful'.
"I have got to say as a manager I enjoyed it and we will take it, a great performance by everybody.
"Strikers are judged outside of the football club by how many goals they score. Sometimes inside they do a lot more than they are given credit for but everybody looks at 'does he score a goal?'
"All week we have been working with all the players on shooting, crossing, getting into the box and being brave. I don't think it's a coincidence that we have scored goals today."