In a tournament where spectacular tennis has been conspicuous by its absence from the women's draw, the two produced a semi-final worthy of the name with a riveting display of power-hitting from the baseline and wily court craft.
Both players got off to a nervous start, each losing their opening service games, before the Russian became the first player to take a set off the American at the All England Club this year by winning the tiebreak 7-4.
Serena levelled the match when a series of aces got her out of trouble when serving at 6-5 in the second before Dementieva, the Olympic singles champion, broke to lead 3-1 in the decider.
The Russian missed match point when a slight netcord helped a Williams volley into play. The American then broke to lead 7-6 and duly held serve to book a place in her fifth final.
She will face her sister Venus or Russian top seed Dinara Safina in Saturday's final
