Benavides was the most highly regarded champion of the four world boxing organisations and was expected to defeat the 29- year-old Briton with ease.
In the early rounds Benavides, 24, looked to have the stronger punch and made a point of finishing each of the three-minute periods with a flourish.
However, McKenzie - knocked out in his previous fight against Rafael Del Valle in May - refused to be intimidated and in a close contest gradually gained confidence. Making use of a sprightly jab and a willingness to take on Benavides at close quarters, McKenzie disturbed the Mexican-born American with his assured approach.
In the 10th round, McKenzie made the decisive move when he connected with a swinging right and Benavides went down, although he seemed to have lost his footing as the punch connected. Coins were thrown into the ring when the referee apparently declined to count, although it was later confirmed that is was, indeed, counted as a knockdown.
Afterwards an emotional McKenzie said: 'It's beautiful to win the world championship in front of my own people. It's like I never lost it. There's been a lot of hard work and a lot of soul- searching, but this is for my little girl, Jessica - she means everything to me.'Reuse content