Even the 33-year-old American edged out his 18-year-old opponent, that was playing at his first Masters semi final, at a 7-6 (7-3) 7-6 (7-4) victory.
Auger-Aliassime was made to rue missed chances, a failure to function out in 53 in the first pair and 5-4 in the next.
Isner fought back to border both sets and might face Roger Federer in the past.
Switzerland’s 20-time Grand Slam champion Federer, 37, assumes on Denis Shapovalov – another Canadian teenager – at the other semi final later on Friday.
Auger-Aliassime, dated 18 and 233 days, could be your youngest man from the championship’s 35-year history to make it to the previous four, with conquered a 14-year listing set by Spanish 17-time key winner Rafael Nadal.
Despite the inevitable frustrations of not even taking his chances against Isner, the Canadian qualifier will reflect favorably on a notable week that has announced his birth among the game’s brightest young talents.
His performances in Florida mean he will be the first male player born in the 2000s to reach the entire world’s top 50, rising around 33rd when the positions are released on Monday.
“Felix will get to the top,” Isner, who has won eight of the 10 places in Miami at tie-breaks, ” said.
“I can not say enough great things about him. He’s got it . He is very humble and wont let success get him”