Tahau slotted two goals in a 7.10 (52) to 6.9 (45) victory at Norwood Oval - the Power's first win over the Crows in four matches.
Tahau has now kicked 23 goals this season - the most of any player in an AFLW home-and-away season.
The Power dynamo equalled Melbourne's Eden Zanker's overall season record with 23 majors in 2023, which included three goals in three finals.
Tahau, a premiership player with the Brisbane Lions who joined Port in 2022 and a year later suffered an injury requiring a knee reconstruction, snapped a goal-of-the-year contender during a precious win.
The Power climbed to 10th on the ladder, just one win behind the seventh-placed Crows, with one game remaining before finals.
Adelaide, with Grace Kelly booting two goals, skipped to a nine-point quarter-time lead, 3.3 to 2.0.
But the Crows lost Niamh Kelly to concussion - the Irish talent left the field after an accidental head clash in a heated push-and-shove following Adelaide's opening goal.
The Crows, led by midfield star Ebony Marinoff's 10 disposals, were remarkably efficient - they scored from all six of their entries inside their attacking 50m zone.
But Port kept in touch on the scoreboard with Tahau slotting a stunning snap when pinned on a boundary line some 30 metres out.
In the second quarter, the floodgates opened with four consecutive Port goals in less than eight minutes of play.
They outscored the Crows 4.2 to 0.3 in the term, with Tahau again featured in a scoring spree capped by an Abbey Dowrick goal.
Dowrick delivered the Power a 14-point advantage, 6.2 to 3.6 at the halftime siren, when yet another melee between the rivals ensued.
Port logged the sole goal in a tense third term, stretching to a commanding 23-point break at three-quarter time, 7.6 to 3.7.
But the Crows, after goals from Anne Hatchard and Rachelle Martin, snuck within 13 points with nine minutes remaining.
And another late major from Caitlin Gould reduced Adelaide's deficit to just seven points with 90 seconds left but neither side scored again.
"It felt like a final," Power captain Justine Mules-Robinson, who was a triple-premiership player with the Crows, told Fox Footy.
"It was a very, very contested game but we just continued to chip away and played our brand of footy."
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