The big question was whether Mascherano was fit enough to play all the 90 minutes, and the answer to that question is yes. But how effectively, is a completely different question, and one which Sampaoli should ponder further.
Sampaoli chose to play him over Lo Celso, the more attacking option. Against a team like Iceland who are regimented, it would have been more productive to play the youngster.
But to his credit, Mascherano was solid when defending for the side and did not make any sort of mistakes.
Hallfredsson, however, was all over the Argentine midfielder. Every time Mascherano had an inkling to drive forward, he found his path impeded by Hallfredsson, and chose to pass it over to Silvio or Meza and retracted back to his position.