Leach scored six tries.
Ngatapa Stags went close to getting on the scoreboard but the Whalers’ defence held firm.
The Stallions were too good for the Panthers, with captain Dylan Williams leading from the front and playmaker Brad Kiwara setting up many of their tries.
Player-coach Jay Casey said their standout younger players were Seth Lundon and Hunter Tangira.
Tangira and Williams both scored a hat-trick of tries.
The Panthers had some of their own positive moments on attack in the second half.
Nick Barbarich, Israel Ngauamo and Fabian Miller scored tries for the Panthers.
On Saturday afternoon, Manutuke Mustangs play Turanga Panthers at 1pm and Seeka Falcons play Ngatapa Stags at 2.30pm.
Paikea Whalers and Waengapu Stallions have the bye.