The Swiss top seed was leading by two sets and was 4-3 ahead with his French opponent about to serve in the third when the rains came down for the second time at 7.15pm.
With further showers falling, play was abandoned for the night just before 8pm.
Earlier in the day Federer and Grosjean had managed just five games of their opening set before a four-and-a-half delay meant the other semi-final between second seed Andy Roddick and Tim Henman’s conqueror, Mario Ancic, was moved to court one.
The American had claimed the first set 6-4 and was a break up at 4-3 in the third, although unseeded Croatian Ancic had break point at 30-40 in the eighth game when rain ended play.
Roddick and Ancic will resume their match on court one at noon today when Federer will also aim to complete his passage to the final on Centre Court.
The women’s final, in which champion Serena Williams is due to defend her title against 17-year-old Russian Maria Sharapova, will follow on Centre Court but not before 2pm.
If Williams is banking on nerves getting the better of her 17-year-old opponent, she will be in for a big disappointment.
In becoming the second youngest female finalist in Wimbledon history, Russian schoolgirl Maria Sharapova has uncovered a steely resolve fostered in her solitary upbringing in a tennis academy in Florida.
That single-minded determination helped her to a remarkable semi-final win over former champion Lindsay Davenport and puts her in good stead to become the first Russian to win the women’s singles title.
The immensely-gifted Sharapova followed up the greatest win of her fledgling career with a full 10 hours of sleep and yesterday confidently looked ahead to taking on the two-time champion.
“I haven’t been nervous throughout the whole tournament,” she said. “I’ve just been enjoying myself so I’m going to go out and do what I’ve been doing for the last six matches, just play my game and enjoy.
“And nerves are part of tennis. I like that part of it, it keeps you motivated, keeps you wanting to be in the situations and get out of them by winning.”
The supremely confident Sharapova has expressed her surprise at reaching her first Grand Slam final at such an early age yet she has always been a fast learner.
The girl from Siberia, who moved to Florida with her father at the age of seven to be fast-tracked to tennis stardom, learned to speak English in just four months.
But it is with a heavy heart that she recalls the harsh existence of her youth. She was separated from her mother for two years while she set out on the trail of tennis champions at the Bollettieri academy.
She also saw little of her father Yuri as he sought work to pay the bills and was forced to live in a dormitory for a year with older girls. It was a Cinderella-like existence which toughened her for the trials ahead.
“When you come to a whole different country and a whole different culture when you’re just seven, everything just takes you by surprise,” she said.
“You hit a wall where you’ve never seen this wall before. I didn’t speak English the first four months I was there so I couldn’t communicate with many of the pople. But I learned English in about four months and then I wasn’t shy.”
The sacrifices are set to pay huge dividends, with Sharapova poised to enter the world’s top 10 if she overcomes Williams, 30 years since the only previous Russian Wimbledon finalist, Olga Morozova, lost to Chris Evert.
The teenager, who fits her school work in between matches, remains unfazed by the sudden attention unleashed on her following her victory over Davenport but still has to pinch herself from time to time.
“What has happened is really incredible,” she admitted.
“Getting to the Wimbledon final is a dream come true.
“It’s an amazing feeling, it gives me goosebumps. But it’s happened so fast that it’s still kind of new to me.”
The Williams sisters were figures in the distance when Sharapova was learning how to hit the ball with venom under the watchful eye of Nick Bollettieri.