The Grecians pegged Stags back through Lee Holmes’ 87th minute equaliser to take the shine off one of Mansfield’s best performances of the season.
Hemmings had fired the home side ahead with a clinical first time finish in the 19th minute.
But they paid the price for a failure to put second half chances away to leave Stags five points off the play-off places.
Hemmings said: “We were by far the better team, we were on the front foot all game.
“I think once the first goal goes in, even before that, we were playing with a lot of confidence and on the front foot so we’ll take confidence from the game knowing that we can go into games and we can dominant teams in that respect.
“We’ve had a lot of chances. I’m guilty of missing a chance and a couple of other chances that I probably should stick a way and see the game out.”
“We’ll take confidence from the game knowing that we can go into games and we can dominant teams in that respect.”
And Hemmings says he was delighted to find the back of the net on a personal level.
He added: “It means a lot to score]because I’ve got high expectations of myself and I think it’s fair to say I’ve not really reached that at the minute and scored the amount of goals I expected.
“I thought I played well today. I thought I worked really hard and played well. Hopefully in the coming weeks there will be more performances and goals to come.”