As Tomas Berdych finally ended his Rod Laver Arena jinx with a four-sets win over David Ferrer, Li looked odds-on to reach a third Melbourne final after tearing past fellow veteran Pennetta.
The Chinese world number four pummelled winners past the Italian as she broke five times and won 62 points to just 37 for her opponent in the 6-2, 6-2 victory.
Li, seeking her second Grand Slam title, is peaking at the right time, with the 67-minute mauling coming after she smashed past Ekaterina Makarova in less than an hour on Sunday.
It followed a verbal volley by coach Carlos Rodriguez after her struggles in the third round, when she was taken to three sets and saved a match point against Lucie Safarova.
"After I saved match point (against Safarova) I have got better, I got a lot of confidence from that and I believed in myself," said the 2011 French Open champion.
Li, 31, will be hot favourite to reach Saturday's final although she faces a new challenge from 19-year-old Bouchard, who announced herself on the world stage by stunning Ana Ivanovic.
Despite a gulf in experience and rankings, the Canadian world number 31, aggressively took the fight to former world number one Ivanovic, now ranked 14th.