After the break, Northland went looking for more and managed to pen Mangere into their own half but they could not quite kill the game off.
Ruddell cut in again from the left-hand side to seal the victory on 63 minutes, but, instead of going for the jugular, Northland seemed to ease off and allowed a consolation goal seven minutes later.
Things became a bit frantic, and a soft penalty gave Mangere some hope - especially as Northland goalkeeper Shane Stanners saw red after the kick due to an altercation.
Max Thomas found space on the right-hand side though and coolly slotted home to put the result beyond doubt.
Head coach Dan Johnston said they were hoping for a strong finish to the year.
"It was another real team performance today. The boys have worked hard all year and our league position reflects that," he said.
"We have three very tough fixtures coming up between now and the end of the season but there is no reason why we can't finish with three wins."
Northland travel to Ngongotaha next weekend for a game on the shores of Lake Rotorua.
Meanwhile the Northland FC women had a tough Premier Division outing against Glenfield Rovers, putting more onus on their home fixture next week.
They went down 2-0 in a fighting effort as they showed a lot of tenacity and steel throughout the contest.
Northland have been working hard in the top women's division and should be rewarded with at least another season in the top flight.
They can secure this on Sunday when they take on Hamilton Wanderers at home. Wanderers have struggled to just three competition points in the season.
