Vitor Pereira's selection was questioned when the teams were announced.
Nine changes, Chris Wood starting after six months out injured and Nottingham 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 ofAston 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.
