Panthers took an early lead through Brian McGrattan, but Steelers’ forward Andreas Valdix tied things up midway through the second session.
Fretter completed the scoring with seven minutes remaining to leave Steelers’ boss Paul Thompson delighted at the halfway stage in the tie.
“As a visiting coach you have to be happy with any lead going into the second leg of a series like this against the Panthers,” Thompson told the Yorkshire Post.
“I give Nottingham a lot of credit, they were down a couple of bodies and played a very solid game and made it difficult for us.
“It’s hard to break down a deep 1-4 and you sometimes need something special to break the deadlock, just like Colton did when he took the puck to the paint – it was a super move and great goal for us.
“It is what you have to do when a team is playing such a defensive game.”
The Panthers’ hopes of establishing a first leg lead were hampered by injuries to key players ahead of the game and they suffered another setback as Jason Williams missed the final two periods.
Corey Neilson’s team looked out on their feet going into the third session, but their rivals failed to take full advantage.
“If I was coaching on the other bench we would have upped the tempo and looked to step on their necks,” Neilson told the Nottingham Post.
“The fact they sat back, I think they missed a trick. I was surprised they didn’t come out hard in the third period.
“I don’t think it was a wise decision. They could have legitimately ended it if they played hard and played well.
“I think they played okay, but if we get a chance to come back with our four lines going with key men back then I like our chances.
“I thought we played pretty well. They had 14 forwards, six ‘D’ and two goalies. That’s a very good, very deep Sheffield team.
“I won’t just take the scoreline going into the second leg, I’ll take it happily right now with that group.”
(Image permission: Karl Denham)