In a battle of former world number ones the momentum shifted in the Belarusian's favour early in the third set when Kerber committed two double faults in a careless service game to hand Azarenka a 2-0 lead.
Azarenka seized the opportunity, consolidating the break in the next game before cruising to the finish line to reach her first final in more than three years.
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"I'm very pleased with how I played today," she said in an on-court interview on a warm night in northern Mexico.
"It was an important match and to see how I can do under pressure against a top player," she said.
"I haven't won many of those in the last couple years so it's good that I'm able to turn it around and pick up my level."
Earlier, defending champion Garbine Muguruza reached the final with a 6-2 6-3 win over Magdalena Rybarikova.
Number two seed Muguruza needed only 76 minutes to progress, with her Slovakian rival seemingly troubled by an injury to her left leg throughout the match.
Rybarikova received a medical timeout after the first seven games, and she had no answer to the Spaniard’s power game.
Azarenka came out the victor in her only previous meeting with Spaniard Muguruza, a hard-fought 7-6(6) 7-6(4) win on the hard courts in Miami in 2016.
(With additional reporting)
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