"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".
The fifth-seeded Azarenka received treatment on her leg during a medical time-out between sets, but it became apparent as the second set began that her movement had become significantly hampered.
Elsewhere, Madison Keys claimed the first clay court title of her career on Sunday with a straight sets defeat of Caroline Wozniacki in the final of the Charleston Open.
"It's unfortunate I couldn't give my best today, but I tried my hardest", a tearful Azarenka said.
Keys closed out the first set with a forehand service return, then broke Puig, the Olympic champion, three times in the decider.
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I ain't trying to shoot [my shot] at her. "She can call my line", he said during the broadcast. He was pronounced dead at the hospital, while the other two men are in stable condition.
Azarenka seized the opportunity, consolidating the break in the next game before reaching her first final in over three years.
In other first round matches on Tuesday, there were wins for the seventh seed Sara Sorribes Tormo, 6-4 6-4 over Christina McHale, and Magda Linette (8), who overcame Aliona Bolsova Zadoinov 2-6 7-6 (7-5) 6-0. The final was supposed to be the climax of who would win Monterrey this year.
Muguruza now holds a 4-2 lead over her Slovakian adversary. She would grit her teeth, grimacing all the while with pain shown throughout her face. She has the momentum, form, and the lead in the head to head.
How could it? She would struggle throughout the third game and had to retire. She'd make her 7th career title and as for Azarenka she was a finalist again, after a three-year drought and could only be glad to have gone deep into the tournament.
Muguruza will start this match as the favourite to win.