Ten-man Plymouth held on for a point against promotion rivals Watford despite Peter Halmosi's dismissal.
Jermaine Easter put Argyle ahead when he met Fallon's cross from the right with a neat finish.
The Hornets levelled immediately when Williamson curled a delightful free-kick into the top left corner.
Watford pushed forward after Halmosi was sent off for his second booking but Darius Henderson headed over and Danny Shittu's effort was hacked clear.
Plymouth manager Paul Sturrock: "We still went with two forwards even when we went down to 10 men because
at this juncture of the season, we have got to try and win
football games.
"We had to change our system and take a winger off but strangely enough we
still got up the football pitch, which was quite pleasing.
"But in the end, a draw
was a fair reflection of the whole game."
Watford boss Aidy Boothroyd: "I think it's definitely a point gained although we are disappointed not win -
especially as we were left playing against 10 men.
"I was disappointed about the goal we conceded. We thought there was a hint of
offside about it, although we haven't seen it again.
"With the pace at the back
we have, we should not have been caught out like that."
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