The match will resume today before the men's final, with Pierce leading by two games to one and holding a break point. Desperate though both crowd and organisers were to have the match played, to hold it over was the only possible decision. Heavy rain had started again, the light was terrible, and the balls so caked with damp clay that it was making play unacceptably awkward.
We saw enough, though, to suggest that Pierce has every chance of becoming the first French woman champion here since Francoise Durr in 1967. In the sort of atmosphere that would test the nerve of the most experienced player, - the crowd was giggly with excitement after sitting around for so long - it was Sanchez, champion here in 1989 and three years Pierce's senior, who looked the more unsettled.
Pierce was on her way immediately, winning the first point with a serene backhand down the line, and had two break points in Sanchez's opening service game. The girl with three passports clearly knew where she was going.
Whatever happens today, Pierce has already done enough with her 6-2, 6-2 defeat of Steffi Graf in the semi-final last week to breathe new life into a women's tennis scene which had long since started to stagnate.
That was no fault of Graf's. If her demeanour here was anything to go by she was not enjoying being so far out on her own any more than the fans were. But what could be done about it? Nothing, except wait for Monica Seles to come back.
Now the need for Seles's return does not seem quite so urgent. In becoming the first player to stop Graf reaching the final of any tournament since February last year, Pierce's world changed forever. Until last Thursday she was thought of first as the victim of a violent father, whose excesses overshadowed almost everything in her life, and only secondly as a tennis player, whose talents, although considerable, were unlikely ever to take her right to the top.
In 58 minutes of blistering tennis, the 19-year-old Pierce took herself on to a new plane altogether, banishing to a great extent the ghosts of her past and offering enough evidence to suggest that if she can maintain the same mental outlook then she could become a real force.
It is a year since Jim Pierce was banned from this tournament and his daughter was able to make a new start. Five months after he last saw her - at the Australian championships - this weekend he has been expressing his regrets over what happened. 'What I did was not for myself but to make her financially independent.' In the end it was independence in the widest sense that she felt she needed.
It is Nick Bollettieri, the man whose work with Seles and Andre Agassi first raised the status of coach to that of guru, who has been responsible for the transformation of Pierce the player. It is fashionable to knock his work, but it has done the trick with Pierce. Together with Sven Groeneveld, a Dutch coach, they make training fun, she says - and there had not been too much of that when her father had been coaching her.
The result is a player who has made a nonsense of her No 12 seeding here, dropping not one set and only 10 games on her way to the final. Even in the patches of indifferent tennis she has played the aura of self-belief has remained intact.
Of Pierce's star quality there is no doubt, and it goes well beyond merely bringing the tennis dress back into fashion. Willowy, blonde, with limpid blue eyes and a face of exquisite delicacy, there is something ethereal about her which has given an added resonance to the most popular headline of the week: Hail Mary. You would think her unique until you meet her mother Yannick and can see what Mary will look like in 25 years' time.
The game here has welcomed her success with a mixture of delight and incredulity - not to mention relief. 'This is great for the future of women's tennis,' Pam Shriver, president of the Women's Tennis Association, said. 'We needed new blood, and I believe that Mary has an important role to play in the years to come.' Starting today.