Argentina, who will be without the rested Lionel Messi, beat Iraq 4-0 on Thursday.
Brazil will be the more concerned team ahead of Tuesday's showdown in Jeddah as they failed to spark against the game Saudis, who almost found themselves a goal up after six minutes, before Casemiro hacked clear.
Jesus saw a goal-bound header brilliantly saved by Saudi keeper Mohammed Al Owais before Neymar slipped him in to score in the 43rd minute.
Tottenham's Lucas Moura almost made it two after another fine pass by Neymar.
Neymar came close himself a few minutes later with a shot from just outside the penalty area.
The Saudis ended the match with 10 men after Al-Owais was sent off with 10 minutes left for handling the ball outside the penalty area when pressured by Richarlison.
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