Kike Sola had given Los Rojillos the lead with his strike in the 84th minute.
The visitors were down to 10 men at that point after Emiliano Armenteros was given a red card in the 78th minute.
But substitute Castro, who replaced Pedro León in the 63rd minute, buried a right-footed spot-kick into the lower left section of the net to earn a point.
Getafe were caught offside seven times.
The two attempts by Ángel Lafita were the most of any Getafe player.
Osasuna enjoyed possession of the ball for 45%.
Rojillos had seven shots, including three on target.
Nino had two shots for Osasuna, more than any of his team-mates.
- Sports & Recreation