Russian champions Zenit St Petersburg, who won all their group stage games, lost to a stoppage time goal at Young Boys in another round of 32 first leg tie.
However, their compatriots Spartak Moscow were on the right end of a comeback, away to Swiss opponents as they bounced back from 2-0 down to win 3-2 at FC Basel. Ajax won 3-0 at Anderlecht while fellow Dutch side Twente Enschede were among several teams who endured freezing conditions in eastern Europe, beating Rubin Kazan 2-0 in Moscow where the temperature hovered around minus 15 Celsius.
Liverpool were held to a goalless draw at Sparta Prague while Lille drew 2-2 at home after a late rally by PSV Eindhoven in a meeting of the French and Dutch league leaders.
Porto, beaten only once in 34 outings in the Portuguese League and Cup and Europa League this season, went ahead in the 58th minute when Rolando stabbed home after a free kick. Sevilla striker Frederic Kanoute levelled in the 65th, also from a free kick, before Colombia midfielder Guarin stole the win with five minutes left as Porto made a happy return to the scene of their 2003 UEFA Cup final win over Celtic.
Ajax made light of Luis Suarez's absence -- the Uruguay forward having been sold to Liverpool in the January transfer window -- as Tony Alderweireld, Christian Eriksen and Mounir El Hamdaoui shared the goals at Anderlecht.
Marcin Wasilewski squandered a 55th minute penalty, one of several opportunities wasted by the hosts, when they were only 1-0 behind.
Liverpool could not field Suarez under UEFA regulations and failed to find the target as they drew 0-0 at Sparta Prague.
Peguy Luyindula scored an 89th minute equaliser to give Paris St Germain a 2-2 draw at BATE Borisov in Minsk, another match played in temperatures well below freezing.
Bayer Leverkusen also had to contend with bitter conditions in Ukraine as they thumped Metalist Kharkiv 4-0.
Eren Derdiyok and Gonzalo Castro scored either side of halftime before Sidney Sam got two more for the Bundesliga side. Metalist's compatriots Dynamo Kiev enjoyed contrasting fortune as they won 4-1 at Besiktas.