It was not until his third match that Mendoza won.
It was until his third match that Mendoza won.
What is the difference between two sentence?
It was not until his third match that Mendoza won.
It was until his third match that Mendoza won.
What is the difference between two sentence?
The first sentence means that Mendoza lost his first two matches and then won his third match. The second sentence means that Mendoza won his first two matches, but lost the third. However, the second sentence would not be used by a native speaker.
It was not until X(time) that Y(event).
is a commonly used construction in English, and could be rephrased as
Z(subject) did not Y(verb phrase) until X(time). (e.g. - Mendoza did not win until his third match.)
However, your second sentence is a form that I have never seen used. I cannot quite get to the bottom of why this is, but one obvious point is that it can be easily rephrased to a more concise form:
Until his third match, Mendoza won.
Furthermore, to me, there should be a certain continuity to Y in
It was until X(time) that Y(state).
For example,
It was until his third match that Mendoza was unhappy.
This makes sense and may be used by native speakers. But winning a match is an event, rather than a continuous state, so I don't think "won" fits in this construction. However, I'm not sure why this is. Hopefully a linguist can enlighten us.
Edit: Looking back at the above sentence, It actually feels wrong to me as well. Perhaps my event vs. state dichotomy was imagined.
In any case, the simplified version would be preferable here. As in:
Mendoza was unhappy until his third match.
Sentence 1 means Mendoza wins starting with his third match.
Sentence 2 does not make sense; it sounds very awkward.
Another way to rephrase #1 is "Mendoza did not win until his third match."