The on-loan Benfica striker finished off a fine counter attack to score into an empty net before the break.
Ryan Mendes should have made it 2-0 but headed Chris Cohen's free-kick over the bar and also fired an effort wide.
Preston, who stay 10th, four points above Forest in 13th, almost levelled through Jordan Hugill's header.
However, he was denied by Reds keeper Dorus De Vries, who made a superb low diving stop to scoop the ball off the line.
And although Mendes missed another chance that would have avoided a nervy finale, the hosts were able to see out a victory which takes them to within 11 points of the play-off places.
Nottingham Forest boss Dougie Freedman:
"I am very pleased - I thought we deserved to win.
"We could have scored a few more, we created a few chances, although it was a bit nervy towards the end and credit to Preston for that.
"I thought we threatened their goal all night from start to finish, but we had to make sure we got the win after four defeats and we did that."
Preston boss Simon Grayson:
"There wasn't much in the first half, I thought we looked quite comfortable and they didn't threaten us too often.
"We were unfortunate for the goal - they broke quickly on the counter and before you know it the ball's in the net.
"We changed it at half-time to give us a bit of a threat going forward because we have to try and win games at this stage of the season."
Nelson Oliveira's ninth goal of the season was enough to earn victory over Preston North End and halt Nottingham Forest's four-game losing streak.