In 'English Grammar In Use' by Raymond Murphy, page (237), he gives the following example provided by its answer:
- Claire comes into the room. She looks absolutely terrified.
You say to her: What’s the matter? You look as if you’ve seen a ghost. /
… as if you saw a ghost.
I have the second edition of "English Grammar in Use" and in Unit 117 As if I can see in exercise 117.2 (page 235) a similar situation solved differently in the Key:
- Christine comes into the room. She looks absolutely terrified.
You say to her: What’s the matter? You look as if you’ve seen a ghost.
The point is that, with some verbs, the past is used to refer to the present. Murphy says on page 234:
After as if we sometimes use the past when we are talking about the present. For example:
- I don't like Norma. She talks as if she knew everything.
Murphy then explains that this is unreal past (i.e. subjunctive) and adds that, if the verb be is used, "were" can be used instead of "was":
- Why do you talk about him as if he were (or was) an old man?
- They treat me as if I were (or was) their own son.
I think that adding "just," as David suggested, is necessary to make "saw" sound like past rather than present.