The Porto defender accidentally passed it into his own net from 45 yards with goalkeeper Diogo Gomes stranded, to cancel out William Gomes’ early opener.
It gave Forest a way back in Portugal just as the hosts threatened to quickly take complete control of the Europa League quarter-final first leg.
“It’s part of the match, it’s part of the game. There was some pressure and some failure in their communication so we ended up scoring,” said Forest boss Vitor Pereira.
Now, victory at the City Ground – where they have already beaten Porto this season – next Thursday would send Forest into their first European semi-final since 1984.
Aston Villa could be waiting for an all-English clash after their 3-1 win in Bologna put them in pole position to progress.
Stefan Ortega had already denied Terem Moffi and Borja Sainz before Porto went ahead, William Gomes finishing at the far post, and he saved again from Moffi in first-half injury time.
Igor Jesus had a goal disallowed after the break, having collided with the goalkeeper, while Ortega’s fine stop denied William Gomes a second.
It meant Forest boss Vitor Pereira, who won two titles with Porto, returned to Estadio do Dragao to claim a vital result after making nine changes – including starting Chris Wood, as the striker made his return after six months out.
Forest remain in a Premier League relegation battle, sitting three points above the drop zone, with Pereira mindful of Sunday’s top-flight visit of Villa.
“We changed some players, why? In two and a half days we are playing against Aston Villa and I have to think about it,” he said.
“If we were certain in the Premier League we would be talking about another match, but I’m pleased with the result, the players gave it their best, they kept it open and we will see what we can do next week.
“We are playing to stay in the Premier League and that has to be taken very seriously. I have to be responsible and we have to add points as quickly as possible to escape the last matches and remain in the Premier League.”
Nottingham Forest analysis: Pereira’s changes pay off with positive result
Vitor Pereira’s selection was questioned when the teams were announced.
Nine changes, Chris Wood starting after six months out injured and Forest without the suspended Elliot Anderson.
At the final whistle, the head coach’s plan had worked perfectly as Forest claimed an impressive draw at Estadio do Dragao to take into next week’s second leg at the City Ground.
With Premier League survival on the line, Pereira had already dismissed talk of priorities in Portugal but it was evident there was already one eye on Sunday’s Premier League visit of Aston Villa.
Porto boss Francesco Farioli made eight changes – as his team try to win their first title in four years – but it was Pereira who was the victor, even with a draw.
Nikola Milenkovic, Igor Jesus, Neco Williams, Omari Hutchinson and Ibrahim Sangare were all introduced in the second half as Forest consolidated the result.
They still rode their luck, early in the first half especially, and Stefan Ortega’s late save from William Gomes ensured the positive result.
The only caution would be Forest have won away at Fenerbahce and Midtjylland in the knockout stage of the competition but lost at home.
But they beat Porto 2-0 at the City Ground in the group phase in October, Sean Dyche’s first game of his brief spell.
Even before then, the aim was to win the Europa League and, after a draw in Portugal, Forest have moved a step closer.
What’s next for these teams?
Nottingham Forest: Aston Villa come to the City Ground in the Premier League on Sunday (14:00) before Porto travel to Nottingham for next Thursday’s Europa League quarter-final second leg (20:00).
Porto: The title chasers go to Estoril on Sunday (20:30) as they prepare for the second leg at the City Ground on Thursday (20:00).
Player of the match
Number: 27
S. Ortega
Average rating
7.85
Porto
(active)
Nottingham Forest
Number:
3
Thiago Silva
Average Rating:
4.87
Number:
52
Martim Fernandes
Average Rating:
4.84
Number:
5
J. Bednarek
Average Rating:
4.69
Number:
99
Diogo Costa
Average Rating:
4.68
Number:
11
Pepê
Average Rating:
4.48
Number:
8
V. Froholdt
Average Rating:
4.48
Number:
7
William
Average Rating:
4.39
Number:
10
Gabri Veiga
Average Rating:
4.35
Number:
42
S. Fofana
Average Rating:
4.33
Number:
17
Borja Sainz
Average Rating:
4.33
Number:
12
Z. Sanusi
Average Rating:
4.31
Number:
13
P. Rosario
Average Rating:
4.27
Number:
29
T. Moffi
Average Rating:
4.26
Number:
22
A. Varela
Average Rating:
4.18
Number:
20
Alberto Costa
Average Rating:
4.14
Number:
27
D. Gül
Average Rating:
4.01
