Porto scored in the first minute of each half to edge ahead in their Champions League tie against Juventus.
Mehdi Taremi pounced on Rodrigo Bentancur’s poor back pass to slide in and convert after only 63 seconds.
Juventus were being outplayed but Adrien Rabiot saw an acrobatic effort pushed away, and Moussa Marega stroked home 19 seconds into the second half.
But Federico Chiesa pulled a goal back on 82 minutes heading into the return leg of the last-16 tie on 9 March.
Chiesa goal could be crucial
Juventus have dominated Serie A, winning the title for the past nine years, but Andrea Pirlo’s side are off the pace this season at home and could not come to terms with an energetic and lively Porto outfit either.
The Portuguese champions pressed from the first whistle and got an immediate reward as Bentancur’s pass under pressure fell short of Wojciech Szczesny allowing Iran international striker Taremi to sneak in and score.
The second half started in similarly calamitous fashion, Wilson Manafa picking out Marega unmarked eight yards out to slip home a finish at the near post.
Porto, winners of the competition under Jose Mourinho in 2004, last reached the quarter-finals two seasons ago and were strong favourites to reach the last eight with eight minutes remaining.
But although Cristiano Ronaldo was kept quiet, Italy international Chiesa broke from midfield and side-footed in a neat finish to give Juventus an important away goal.