Martim Fernandes' freak own goal gifted Nottingham Forest a route to a first European semi-final in over 40 years.
2025/2026 UEFA Europa League
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Match Report
The Porto defender 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.
Now, victory at the City Ground - where they have already beaten Porto this season - next Thursday will 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 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 Aston Villa.
Line-ups
Porto XI: Thiago Silva, S.Fofana, Bednarek, Diogo Costa, Pablo Rosario, Zaidu Sanusi, Terem Moffi, Sainz, Gabri Veiga, Martim Fernandes, William Gomes
Subs: Cláudio Ramos, João Costa, Pepê, Francisco Moura, Kiwior, Alan Varela, Dominik Prpić, Victor Froholdt, Rodrigo Mora, Alberto Costa, Deniz Gül, Tiago Silva
Nottingham Forest XI: Wood, Ortega, Gibbs-White, Ryan Yates, Dominguez, Dan Ndoye, Dilane Bakwa, Morato, McAtee, Zach Abbott, Murillo
Subs: Sels, Aina, Sangare, Milenkovic, Hudson-Odoi, Lorenzo Lucca, Neco Williams, Igor Jesus, Omari Hutchinson, Justin Hanks, Jimmy Sinclair, Archie Whitehall