DONETSK, Ukraine — Euro 2012 has reached the semifinals, and few would be surprised Wednesday if the Spain-Portugal match was decided by a pass or a goal from Andrés Iniesta, the little man of big moments.

He is 5 feet 7 inches, humble, pale and balding at 28, but Iniesta’s natural reticence is balanced by a chimney sweep’s comfort in tight spaces. It is evident in his vision and balance and agility, in his movement and Euclidean mastery of the geometric passing that sustains Spain and his league team, Barcelona.

He has an elusive gust of speed, too, when creativity alone is insufficient. The Illusionist, Iniesta is sometimes called, able to play everywhere in midfield, often appearing from nowhere.

In the quarterfinals, France was so concerned about Iniesta that it used two right backs to blunt him instead of one. In Spain’s opening match, Iniesta awaited one pass with five Italians surrounding him. A photograph of the play became popular in Spain, Iniesta encircled as if about to be besieged for an autograph, or arrested.