Tigres kept alive their dream of becoming the first Mexican side to win the Copa Libertadores after scoring a crucial away goal in a 2-1 defeat to Brazilian side Internacional.
Defender Hugo Ayala was the hero and villain for the Mexicans, scoring a potentially vital goal on 23 minutes to haul his side back into the tie after Andres D'Alessandro and Valdivia had put Inter 2-0 up after 10 minutes.
Ayala's joy was tempered however by a 58th-minute red card which will rule him out of the second leg next week in Mexico.
Tigres are attempting to make history by becoming the first Mexican team to triumph in the most prestigious club football tournament in Latin America.
The club has invested heavily in assembling a squad capable of challenging for the Libertadores crown, with French international striker Andre-Pierre Gignac signing from Marseille earlier this year.
Earlier, Brazilian midfielder Valdivia had scored the pick of the night's goals, lofting in a chip from the edge of the area to give Inter a 2-0 lead before Ayala pulled a goal back for Tigres.
The winner will face either Argentinian giants River Plate or Guarani of Paraguay in the final.
River took a 2-0 first leg lead against Guarani in Buenos Aires on Tuesday.