They took the lead for the first time early in the fourth quarter and goal shoot Aliyah Dunn, who missed just one of her 33 shots, scored in the last second to level the match at 57-57 and force extra time.
Jane Watson was lively for the Tactix defence — Mystics goal shoot Grace Nweke missed 10 of her 69 shots — but was restricted to 45 minutes as she returns from injury.
Watson and goal attack Te Paea Selby-Rickit (29 from 33) stepped up for the Tactix as the game hung in the balance in the final quarter.
But the Mystics secured their 11th win in 15 games this season, with goal defence Phoenix Karaka — named player of the match — and wing attack Peta Toeava prominent.
The Mystics started strongly, quickly out to a 6-1 lead on the way to an 18-13 advantage after the first quarter. Centre Tayla Earle and Toeava worked together smartly to work the ball to Nweke at speed.
Watson’s introduction in the second quarter helped the Tactix close the gap to just two goals at halftime.
The Mystics edged the margin out to three heading into the final quarter before the Tactix fought back to threaten an upset before losing after six minutes of extra time.