Schalke goalkeeper Ralf Faehrmann saved one penalty but was beaten by another as Porto salvaged a 1-1 draw in their Champions League-opening game on Tuesday.
Brazilian midfielder Otavio scored the equalizing penalty with 15 minutes remaining, despite complaints from the home side that Moussa Marega fell under minimal contact from Naldo.
The Schalke defender was also at fault for the first penalty after a hand-ball in the 12th minute.
Porto midfielders Hector Herrera, left, and Danilo react after the Champions League group D soccer match between FC Schalke 04 and FC Porto at the Arena AufSchalke in Gelsenkirchen, Germany, Tuesday, Sept. 18, 2018. (AP PhotoMartin Meissner)
However, Faehrmann guessed correctly, diving to the right to push Alex Telles' spot kick around the post.
Schalke's Breel Embolo put his team ahead in the 64th, slotting the ball inside the far post after some good work from Nabil Bentaleb and Weston McKennie.
But the home side was left ruing referee Jesus Gil Manzano's decision to award the second penalty.
Porto forward Jesus Corona, left, and Schalke defender Naldo go for a header during the Champions League group D soccer match between FC Schalke 04 and FC Porto at the Arena AufSchalke in Gelsenkirchen, Germany, Tuesday, Sept. 18, 2018. (AP PhotoMartin Meissner)