Francisco Moura's equaliser was his first goal for Porto
Porto and Roma, two of the pre-season favourites to win the Europa League, drew the first leg of their knockout-phase play-off.
Claudio Ranieri's visitors led just before half-time when Zeki Celik reacted quickly and hooked in from close range from Artem Dovbyk's knock-on.
But Porto levelled when Roma failed to deal with Diogo Costa's long ball downfield and Francisco Moura scored from the edge of the box via a deflection off Celik.
Roma had midfielder Bryan Cristante sent off for two bookings, meaning he will miss the second leg next Thursday.
Opta had made Porto pre-season favourites to win the Europa League - a 17.8% shot - with Roma fifth favourites at 8.2%
But neither side managed to finish in the top eight in the group phase, so failed to qualify automatically for the last 16.
