Williams did not even have to pick up a racquet in order to book her spot after fifth seed Jamie Hampton was forced to withdraw after suffering a hip injury in practice.
By contrast, Serb Ivanovic resisted a second-set fightback from third seed Kirsten Flipkens to qualify 6-0 7-6 (7/3).
Prior to the tournament Williams had targeted at least a place in the final as she looks for her first title since Luxembourg in September 2012 with the American having to contend with the debilitating Sjogren's syndrome in recent times.
Now ranked 47, the 33-year-old would have expected a tough workout against Hampton, who is ranked 19 places above her, in what would have been the pair's first meeting.
While admitting she was mightily disappointed, Hampton wanted to ensure she was taking no risks with the Australian Open starting on January 13.
In quotes on the WTA website, the American said: "At the end of my warm-up this morning I took a couple of extra swing volleys and I just jammed my hip.
"I think I'll be fine for the Australian Open if I take the proper steps to recover.
"It's incredibly disappointing. I wanted the opportunity to play such a great champion and have a chance at making the finals and winning my first title, but that's how the cookie crumbles unfortunately."
It meant the crowd were denied one of the big matches of the tournament and instead all eyes were on second seed Ivanovic.
The 26-year-old stormed through the first set in 21 minutes before grinding through what turned out to be the decider with her opponent refusing to give way.
Ivanovic said: "The first set was really almost without mistakes - I served well, hit the ball well and played very aggressive too.
"The second set I felt was good for me too, but she started to serve better and put a lot more pressure on me, but I managed to serve well too and played well at the end.
"I expected a tough match today and it turned out to be a really tough second set."
Williams leads Ivanovic 8-1 in head to heads and said: "We all know what Venus is capable of, and she's been showing some good form this week too.
"I've struggled with both Serena and Venus in the past. They both have a big serve, and it can be overwhelming at times.
"But over the years you get used to it and become more calm. There's no doubt it'll be a very, very tough match, but it's a matter of still doing the things I've worked on.
"We've had some tough matches in the past and I'm really looking forward to that final challenge."