Lucic-Baroni is clearly a great survivor, but the stress of playing 10 matches (singles and doubles) in 11 days was still mounting up, judging by the heavy strapping on her left leg. Serena was in unforgiving form - as she had been against Johanna Konta in the quarter-finals - and barely missed a ball as she eased through 6-2, 6-1 in just 50 minutes.
Venus, 36, had to scrap much harder as she took on the muscular hitting of Coco Vandeweghe.
All four semifinalists were the sort of players who look for quick kills - the only way to play on the slickest courts we have seen at a major for years - but Vandeweghe is especially trigger-happy.
She swung like Joe DiMaggio, stealing the first set on a tie-break before Venus brought her experience to bear. A tactical adjustment on second serve, which she started striking with a little more pace, helped Venus save 12 of the 13 break points she faced in the match.
She celebrated by performing a dainty little dance, full of girlish enthusiasm and knock-kneed delight.
"I only saw a twirl," said Serena later, "but it was a double turn. I was like, 'Gosh, she's doing that on her dance team'. Quite impressive."
Serena was unusually relaxed after the match, saying: "I just can't help but feel like it's a win-win situation for me."
Either she will collect her 23rd major title, to move into the clear space between Steffi Graf (22) and Margaret Court (24).
Or Venus will earn the reward that her determination deserves. Apart from being one of the oldest players on tour, she also suffers from Sjogren's Syndrome, an incurable auto-immune disease.
"I've been there when she was down and out of it," said Serena.
"We lived together. I know what she went through with her illness. This probably is the moment of our careers so far. I never lost hope of us being able to play each other in a final, although it was hard because we're usually on the same side of the draw. This is something where I couldn't write a better ending."
Williams-Williams finals were a regular feature of the past decade, but have not been seen at any level since 2009. In the old days, the sisters always had to bat away claims that the result was arranged over breakfast. Yet the one-sidedness of the series hardly suggests collusion.
In eight major finals, Serena has won six to Venus's two. She must be favourite again here, having won all 12 sets she has played to date, and dispatched Konta in comprehensive style.
Not that Venus is ready to cede the foreground just yet. "When I'm playing on the court with her, I think I'm playing the best competitor in the game," Venus said. "But I don't think I'm chump change either."
Previous slams
US Open 2001
Venus won 6-2, 6-4
French Open 2002
Serena won 7-5, 6-3
Wimbledon 2002
Serena won 7-6, 6-3
US Open 2002
Serena won 6-4, 6-3
Australian Open 2003
Serena won 7-6, 3-6, 6-4
Wimbledon 2003
Serena won 4-6, 6-4, 6-2
Wimbledon 2008
Venus won 7-5, 6-4
Wimbledon 2009
Serena won 7-6, 6-2
Total wins: Serena 6, Venus 2
