The world No1 was made to fight all the way by the Chinese 16th seed before eventually reaching a fifth Melbourne final with a 7-6 (7-4), 7-6 (7-1) win.
But while Williams toiled, wildcard Henin enjoyed a somewhat easier route to tomorrow’s final, breezing past the unseeded Zheng Jie 6-1, 6-0 in her first Grand Slam event dince returning from an 18-month retirement.
Williams has won all four of her previous final appearances at Melbourne and is gunning for a 12th Grand Slam title which would equal the mark set by Billie-Jean King, who will be there herself to witness it.
“That’s the goal,” Williams said. “I have a long career to keep trying to do it, but if it doesn’t happen this year then I’ll keep trying.
“I am happy I was able to pull it out, it was really close. I wasn’t at my best today but I’m still here – which is shocking – and I’m just going to do whatever I can to stay.
“I had so many match points and I blew it. I knew on serve [in the tie-break] I had the chance to close it out and I did. I had to because she is an amazing fighter.”
Henin, meanwhile, is now just one match away from emulating the feat of fellow Belgian Kim Clijsters, who won the US Open last September in her first Grand Slam after coming out of retirement.
Having finished Zheng off in just 51 minutes, she will undoubtedly be the fresher of the two come tomorrow, but the former world No1 is simply just happy to be there.
“I was curious about how I would feel. Today was perfect ¬– it was good to have a pretty easy match,” Henin said.
“I can’t wait for the final. It’s an amazing feeling to have the chance to play another final in Melbourne. It’s fantastic for me.”
Meanwhile, Britain’s Laura Robson cruised into the semi-final of the girls’ singles after a 6-1, 6-0 victory over American Ester Goldfeld. She now plays 17-year-old Czech Kristyna Pliskova.