The Hurricanes head the table with 30 points from seven games, ahead of the Chiefs on 27 points from their eight fixtures and the third-placed Blues, who have 25 from eight.
The home side roared into a 14-0 lead in Wellington as Harkin and Billy Proctor scored, and secured their bonus-point victory after tries from Fehi Fineanganofo, Cam Roigard and Asafo Aumua.
"The Blues came with a lot to play for and a lot of motivation," Harkin told Stan Sport. "It was a game we knew we would be tested up front, they want to bang the front door down. It was a case of winning the gain line and just trying to deprive them of the ball for long periods."
Damian McKenzie became the Chiefs' all-time record try-scorer in Super Rugby with a double against Moana Pasifika, taking his career tally to 44 and ahead of Sitiveni Sivivatu.
The visitors ran in 10 tries in Rotorua in a dominant display after the fixture was moved when Moana Pasifika failed to find a sponsor to take the game to Tonga as originally planned.
Quinn Tupaea, Kyren Taumoefolau and Tyrone Thompson all managed two tries each to go with tries for Samipeni Finau and Abraham Pole.
"We are just really happy with the win today," McKenzie said. "We created a lot of opportunities in the game, we know we are not the finished product, we have shown glimpses of amazing stuff in an 80-minute period and then there is some stuff where we definitely need to improve."
