In what was a rematch of the Australian Open final in January, the Chinese world number two was pushed to a deciding set but managed to fend off the 12th-seeded Slovak 6-3 4-6 6-3.
The pair made hard work of their quarter-final clash, with 48 winners hit against 110 unforced errors, and Li doubled Cibulkova's winner count (32-16) while the latter had just eight fewer unforced errors (59-51).
Li's win saw her reach the final four at the event in California for the first time since 2007, when the tournament was known as the Pacific Life Open.
Next up for the two-time major winner Li is Italian Flavia Pennetta, who won a see-sawing quarter-final over American Sloane Stephens.
Pennetta, seeded 20th, outlasted 17th seed Stephens 6-4 5-7 6-4, with the Australian Open quarter-finalist coming from 3-0 and break point down to triumph.
The first set was straightforward - with one break of the Stephens serve enough to get Pennetta ahead, but the second was a different story, littered by seven breaks.
Pennetta served for a two-set win at 5-4, but after a consultation with her coach, could not serve it out, and it would be the first of six consecutive games to Stephens, who rocketed out to a handy lead.
But the wily Pennetta fought back brilliantly, breaking Stephens on her third break point in the fifth game, and then breaking to love in the ninth game to have the opportunity to serve out the match once more.
And despite some grit from Stephens to save four match points, including three straight from 0-40 down, Pennetta sealed her progression to the final four.
Li and Pennetta have split their four career meetings 2-2, with the Chinese claiming recent honours in their quarter-final at Melbourne Park 6-2 6-2.