I'd say Pacos are lucky to be down 1-0, but Porto haven't been impressive. This has been a pretty sloppy game with a lot of disjointed play through the middle and lots of lunging tackles in central areas.
Stephen hasn't had a strong half, made a few passes off-target or into traffic that lost possession and has been on the wrong side of the ball for a lot of Porto counter-attacks. Also picked up a yellow. Still, a lot of the forward play has gone through him and you can see his talent for one-touch passing. He's not shy about pressing into space but as I said his positioning hasn't been great. However, the team doesn't seem to be re-shaping very well and Porto appear to be deliberately flooding the middle so that's not just him.
Pacos have gotten deep with possession but made the wrong choices and haven't had any clear-cut chances.