Toby Peacock made it 3-0 early in the second spell, before Maungakaramea launched their impressive comeback.
But Webb was disappointed that the match finished when it did, with his team still a goal in arrears.
"Another five minutes and we would have scored a couple more and we'd be the ones through to the final," Webb said.
"In the end, we didn't really deserve to, though; we started poorly and that's something we'll have to address before we play Bream Bay this weekend."
Maungakaramea now take on the winners of the third and fourth playoff, Bream Bay, on Saturday, with the winners going on to play Springfield in the final.
"At least we've got another shot at reaching the final. Hopefully, we can take a few positives from this game and build on it and hopefully we'll get another crack at them in the final," Webb said.
On Monday night the women's premier semifinalists were confirmed when Springfield beat Kamo High School 6-0 and Old Girls squeaked past Whangarei Girls High School 1-0.
The results mean that top qualifiers Springfield take on Hikurangi, while Old Girls play Maungakaramea in the other match.