The former Spain international tucked away the equaliser in the 63rd minute, and the outcome might have been even better for the German side if Junmin Hao had tucked away a chance in injury-time which was saved by Vicente Guaita.
The visitors were then reduced to 10 men at the death with the dismissal of Lukas Schmitz.
Valencia had plenty of chances to put the game — and potentially the tie — out of reach after Roberto Soldado put them ahead in the first half, however they could not take advantage and will face a tough trip to Gelsenkirchen.
Both sides attacked from the off and Guaita was called into action in the fourth minute when Jose Manuel Jurado swung in a free-kick from the left forcing the Valencia goalkeeper to punch the ball away under pressure.
The visitors should have taken the lead in the ninth minute when Klaas-Jan Huntelaar found himself unmarked as Valencia appealed for offside but he completely miskicked.
However, it was the hosts who took the lead. Jeremy Mathieu overlapped on the left wing and crossed to the near post where Soldado lost his marker, and the striker sent a first-time right-footed shot into the bottom right corner.
Schalke kept plugging away and Guaita had to be alert to push Peer Kluge’s looping header on to the bar, but they were having problems dealing with Valencia’s attacking play.
Tino Costa unleashed a fierce shot from long range which startled Manuel Neuer as Valencia ended the first half in the ascendancy.
Ever Banega’s ball across goal was not anticipated and it went inches wide before Schalke had a good chance to equalise when Raul brought down Neuer’s goal kick and unleashed a shot from the edge of the area, forcing Guaita to dive to his right to push the ball away.
Aduriz again lost his marker in the area but his shot was more like a backpass and Valencia were penalised when Raul equalised. The ball was played in from the left by Jurado and Raul nipped across David Navarro, took a touch and finished under the keeper.
Ricardo Costa played a poor backpass with Raul lurking, which the goalkeeper had to be alert to sweep away, and Valencia must have been frustrated to find themselves level given their dominance of scoring chances.
Schalke were a far different proposition in the second half and they had a chance to take a 2-1 lead in the tie.
Hao found himself with just the goalkeeper to beat. He unleashed a firm, low shot which Guaita did well to turn aside before Schmitz was sent off after the referee was alerted by his officials that he was booked twice.
Guaita, Miguel, Navarro, Ricardo Costa, Mathieu (Alba 78), Banega (Vicente 68), Topal, Costa, Dominguez (Joaquin 68), Soldado, Aduriz.
Neuer, Uchida, Howedes, Metzelder, Schmitz, Farfan (Draxler 79), Kluge, Matip, Jurado (Edu 83), Raul, Huntelaar (Hao 90).
Referee: Alexei Nikolaev (Moscow).