The Mexican international made it two goals in as many games for his new side, which is off to a perfect start in La Liga, but he was forced off the field just after halftime.
Dos Santos, who scored an equalizer and assisted on the winner in Villarreal's season-opening win over Almeria, handled spot-kick duties after Jauma Costa was fouled in the area on a sliding challenge by Gilberto Garcia. Dos Santos put his left-footed penalty into the lower left corner to notch his second goal in as many games.
Dos Santos was forced out of the match just after halftime with an undisclosed injury, which Mexico will hope is not serious considering El Tri has two vital World Cup qualifying matches coming up on Sept. 6 and 10 against Honduras and the USA, respectively. He jogged off the field on his own power in the 47th minute to make way for Jeremy Perbet, who assisted on Cani's 83rd-minute winner.
Fellow Mexican international Javier Aquino started and played all 90 minutes for Villarreal, which will play at Osasuna in its final match before the international break.