Jackson (21-5) fell behind early, surged to the lead with a dominating second quarter, and they held off a late Eastlake (15-11) challenge to advance.
The Wolves led 19-12 after one quarter, but the Timberwolves took the lead for good with a 21-6 advantage in the second quarter.
Eastlake climbed back to within one point just two minutes from then end, but Jackson head off that challenge.
The Timberwolves’ reward is an 8 a.m. Saturday match against the Federal Way-Woodinville winner.
“It is definitely worth (waking up early),” said Jackson coach Jeannie Boyer. “Once – in 2007 – we got eighth place. It’s a history-making moment for our program.”
Sierra Anderson led Jackson with 18 points. Kendra Morrison led all scorers with 31.