The relegation-haunted Gulls got off to a flying start with on-loan Notts County midfielder Joss Labadie heading them into a second-minute lead. Top scorer Rene Howe took his tally to 16 goals for the season by doubling Torquay's lead in the eighth minute by deflecting on-loan Sheffield United winger Jordan Chapell's goal-bound shot past Chesterfield keeper Tommy Lee.
Liam Cooper's 77th-minute reply was too late in the game for the Spireites as United held on for an important three points.
Knill said of his first win as Gulls boss: "It was coming, we have drawn the last two and I thought we should have had more, and now we have got that all-important win."
Knill added: "It was a massive win. We have been playing alright, we just haven't got the three points to show for it and tonight we have. The two away games that we have had, we came away thinking we should have had three points from both of those.
"It was a great start, just what you need and to be fair it was a great goal. Probably when you watch it back you will see that. Great passing, great movement, great delivery and then a great header from Joss. So that gets you going and I'm never one for resting on my laurels and sometimes you can score too early.
"Then we score a second and everyone is thinking 'great, it's going to be easy from now on'.
"But you know when you look at the quality in Chesterfield's side it's not going to be easy and you have to dig in and we did that when we had to and right up until the end. I am delighted with them, but now we must go again because there are still seven matches to go. The next one here is on Saturday and another big game, York, so we go again."
Chesterfield boss Paul Cook said: "Our game plan and everything else went out the window in the first eight minutes. We knew Torquay would be fighting for their lives. We had them watched on Saturday at Southend and they played really well.
"Unfortunately for us we did not start the game in any shape or form, we were second best for long periods and we end up getting 2-0 down and it's hard to come back from that. We did give ourselves a little lifeline in the second half and, to be fair to the players, they did keep working at it and kept trying, but the game had gone by then."