If you have BSD or GNU tar, you can do this:
mkdir -p "$DEST" && wget -O- "$URL" | tar --strip-components 1 -xvzf- -C "$DEST"
Since GNU tar has
--strip-components, but that's not a standard solution. Anyway, you can't really do this with a single pipeline since you have to have the directory already, and there are perfectly good ways of doing this if you're willing to give up on the whole single pipeline anyway.
mkdir -p "$DEST" &&
cd "$DEST" &&
wget -O- "$URL" | tar -xvzf-
cd * && # Assumes the result only has one directory
mv * .. # Assumes no dotfiles
You can resolve issues of dotfiles and tars of multiple directories by tweaking this answer, if necessary.