Lemieux’s explosive punching power was on full display as he floored N’Dam with a left in the second round, then put him down again twice in the fifth round and again in the seventh.
Two judges scored the bout 115-109 while the third saw it 114-110 for Lemieux, who improved to 34-2 with 31 knockouts. N’Dam fell to 31-2 with 18 wins inside the distance.
As in a world title fight loss to Peter Quillin in 2012 – when he was knocked down six times – Cameroon-born N’Dam showed his ability to absorb punishment.
After going down the first time to a hard left hook he bounced up quickly, and although he seemed to be in trouble late in the round he came back strong in the third.
Lemieux dropped N’Dam with another left hook early in the fifth — then floored him again with another left later in the round. After going down to another left hook in the seventh, N’Dam didn’t again appear to be in trouble.
In lifting the title that was stripped from American Jermain Taylor – who is facing a number of legal issues – Lemieux staked his claim to elite status in one of boxing hottest divisions.
The victory puts the 26-year-old Canadian in the frame for a fight with either unbeaten World Boxing Association champion Gennady Golovkin of Kazakhstan or even Puerto Rican star Miguel Cotto.
Cotto, who destroyed Australian Daniel Geale in four rounds on June 6, is expected to take on Mexico’s Saul “Canelo” Alvarez later this year, with Lemieux now a potential foe for the winner of that fight.