Ronaldo was sent off for reacting to a shove by Carlos Gurpegi and then a confrontation with Ander Iturraspe in the 75th minute, although he appeared to be more sinned against than sinner.
Only a minute earlier Athletic had scored a brilliant equaliser through substitute Ibai with only his second touch after coming on, firing in a bouncing ball from the edge of the area.
Madrid held on for a point, having gone ahead after 65 minutes through striker Jese on his first league start, but the loss of Ronaldo now through suspension, for a possible three games, could well have an impact in the Primera Division title race.
"We played well. It was a high intensity match and we hardly let them have any chances. We did especially well in the second half. It could have been different because we scored first and dominated the match afterwards. Athletic Bilbao scored a fantastic equaliser, but overall we are going away satisfied with how we played," said Real coach Carlo Ancelotti.
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