The winger scored a cracking solo goal for his side, which couldn't hold on to the lead.
On 24 minutes, dos Santos received the ball on the right wing, cut towards the box, beat his defender, then sent an unstoppable curling left-footer into the far corner. The goal was his third of the season.
However, the visiting side came back with three goals in the final 20 minutes to claim the win. Diego Castro scored from the spot to equalize in the 71st minute, before Adrián Colunga gave his side the lead in the 82nd and then scored an insurance goal in the 86th minute.
Mallorca remains in deep relegation trouble, sitting second from bottom in La Liga, seven points from safety.