American McHale won an undulating affair against France's Garcia 3-6 6-2 7-5 in Acapulco, catapulting her into her first final at the WTA International event.
Garcia had the early break in the deciding set with a 2-0 lead, but could not convert her dominance into anything greater as McHale broke back for 2-2.
In a titanic 12th game on the Garcia serve, McHale wasted five match points before finally sealing the match on her sixth opportunity.
McHale will meet top seed Dominika Cibulkova in the title decider of the hard-court event, after the Slovakian was given a comfortable progression through her semi-final with China's Zhang Shuai.
Zhang, the eighth seed, retired with an arm injury when Cibulkova was leading 4-2 in the first set, with the Australian Open finalist spending just 27 minutes on court in Mexico.
Cibulkova has won both of her career meetings with McHale, winning in three sets on hard courts in Stanford in 2011, before chalking up a straight sets win on clay in Brussels in 2012.
McHale, Cibulkova into Acapulco final
