Alabaster held on to the number two spot overall for the series, while Motueka's Roma Edwards won the battle with Te Kuiti's Sam Kelly to claim third overall.
"It feels great to win this. I was crying inside my helmet on that last lap. I didn't know if I would even make it here to race today because of a few difficult personal circumstances. I'm sad my dad couldn't be here today," Rampton said.
Meanwhile, in the four-round men's championship, Hamilton's Kayne Lamont, Takaka's Hamish Harwood, and Mangakino's Maximus Purvis maintained their respective class leads at the second of four rounds of the competition.
Lamont was not as dominant in the premier MX1 class at Rotorua as he had been at round one in Taranaki – he was unbeaten in Taranaki but did not win a single race in Rotorua – however, his 3-2-2 score-card was enough for him to finish the day third overall and hold onto the championship lead.
His advantage has been reduced from 15 points to nine, with Australian visitor Kirk Gibbs still second overall, while defending national champion Cody Cooper, from Mount Maunganui, slipped from second equal (level with Gibbs) to third overall.
Gibbs was top MX1 rider at Rotorua, thanks to a 1-3-1 score-card, while Cooper was second best, finishing 2-1-4.
Former South Islander Harwood, now based in Royal Heights, West Auckland, was in dynamic form.
He was again unbeaten in the MX2 (250cc) class and the "ironman rider" then took a 300cc version of his bike to finish the day sixth overall against the 450cc riders in the MX1 grade as well.
Harwood finished the day 13 points clear of the equal runners-up, visiting Australian Jay Wilson and Taupo's national cross-country champion Brad Groombridge, in the MX2 class.
With six wins from six starts in the MX2 class, Harwood now has an impressive 28-point advantage over Groombridge.
In the National 125cc class, Purvis was unbeatable.
Visiting Australian Mason Semmens finished runner-up each time but he is now 12 points behind Purvis with two rounds remaining.
Third best in the 125cc class standings after round two is Rotorua's Joshua Bourke-Palmer, 38 points behind Semmens.
The series will continue with rounds in Hawke's Bay on March 11 and Taupo on March 24.