Errani was coming off a career breakthrough, defeating Agnieszka Radwanska for her first win over a Top 5 player in the quarterfinals. But there was no such breakthrough in the stars in the semifinals, as the No.1-seeded Williams totally took it to the No.5-seeded Errani with some incredible numbers, blasting 40 winners to just 12 unforced errors, allowing her opponent just 16 points in the match.
In the end Errani just didn't have any answers - Williams blasted an ace to close it out, 60 61.
"Those stats are really good, and very consistent," Williams said. "But for me I didn't go out there and feel great - for me, it was more like let's just see what happens and just try to do the best I can.
"Sara's a really great girl. I really, really like her. I love her fighting spirit. I really like her as a person. But when you go out on the court, you just have to play and forget about who you're playing."
Williams is now through to her 20th Grand Slam final, going 15-4 in her first 19 - but this one may be even more special, as it's only her second French Open final - she won the title here in 2002.
"Gosh, that was a long time ago," Williams said. "I was really surprised that day, for sure. I didn't go into that match expecting to win. I just thought, 'Hey, I'm in the final, let's see what happens.'"
Did she keep her dress from that final? "Yeah. I have all my Grand Slam dresses."
Williams will go into the final with some particularly strong momentum - she is on a 30-match winning streak, the longest of her career and the third-longest of the new millennium, after Venus Williams' 35-match winning streak in 2000 and Justine Henin's 32-match winning streak across 2007 and 2008.
"I"m just really focused right now," Williams said of her recent form. "I want to do the best I can. I want to give myself every opportunity to do that. That's all I want. But even if that means I lose, at least I know I have done the best I can, and it's okay. But as long as I give that effort, it feels better.
"It can happen to anyone on any day. That's why every day I'm trying to do the best I can. And when I'm not, I try to fight through it, because my forehand, backhand, serve - anything could happen."
Williams' 15 Grand Slams include five Australian Opens (2003, 2005, 2007, 2009 and 2010), one French (2002), five Wimbledons (2002, 2003, 2009, 2010 and 2012) and four US Opens (1999, 2002, 2008 and 2012). Her losses came at the US Open in 2001 (to Venus Williams), Wimbledon in 2004 (to Maria Sharapova), Wimbledon in 2008 (to Venus Williams) and the US Open in 2011 (to Sam Stosur).
What would another French Open title mean to her? "It would be awesome for me," she said. "I don't think there's anything that can describe how happy I would be. But right now it's still a dream - I still have another match to play, hopefully to win. It's still two people fighting for the championship."