Torquay substitute Jordan Chappell reduced the deficit with a close range 70th minute strike before Constable teed up fellow sub Asa Hall to make it 3-1 at the second attempt in the 78th minute.
"It was very disappointing but you just have to look at their quality," Knill said.
"I thought it was a fairly even game in the first half and if anything we shaded it but in the second half their quality just outshone ours.
"I thought we played pretty well. We knew we would have to compete and we did. Obviously the conditions were difficult and we played well to the conditions.
"Their keeper made more saves than ours and their goal area was busier than ours. I am not going to say we were happy but we were happy that we competed and made a game of it.
"They probably had more luck than us, for example when Constable comes on, hits a wonder strike and it goes in the back of the net.
"Callum Ball hits a wonder for us and it hits the bar and that sort of thing made a whole lot of difference."