Davies was relieved the frontman was still on the pitch, though, as he secured a 2-1 win and set Forest back on a winning course after last week's loss to Derby.
Davies said: "Yes, we were going to make a substitution before he scored. Sometimes it works out for you and sometimes it doesn't - but it did today.
"As for the penalty, it was a soft one and if I was their manager Alan Irvine I would have been very disappointed by it.
"I was just pleased that we showed the character to win what was a very difficult game against a team who had won four out of their last five matches and were clearly working very hard for a new manager.
"It was a good test for us, having lost our first game in 20 to our nearest and dearest last weekend. But it was important for us to dig in and show the mettle we needed to come off the pitch with three points."
Forest, maybe carrying a hangover from that defeat by Derby, were not their usual fluent selves in the early stages but got the big break of a penalty after Blackstock's shot struck Wednesday skipper Darren Purse on the back as he tried to block it. Purse was penalised for handball.
Blackstock sent Wednesday goalkeeper Lee Grant the wrong way from the spot but Forest did not prosper from their good fortune and the Owls more than held their own until they equalised in the 74th minute.
Substitute Etienne Esajas fired a shot across goal and Luke Varney was left unmarked following a ricochet to shoot past Forest goalkeeper Lee Camp.
But five minutes later Forest were in front for a second time when Chris Cohen's free-kick was not dealt with by the Wednesday defence and when the ball wriggled away from Grant, Blackstock gleefully swept in his second goal.
It was rough justice on Wednesday and manager Irvine argued: "I thought we deserved to get something out of the game.
"There was only one person in the ground who thought it was a penalty because the shot clearly struck Darren Purse on the back. It knocked us out of our stride for 10 or 15 minutes.
"But we talked about a few things at half-time and were in the ascendancy for the second half. I thought we might actually go on and win it because we were on the front when we scored the equaliser.
"But when you put into context how good a side Forest are, we can take a lot of heart from the performance. If we perform like that in our other games we will win more than we lose."