Munetaka Murakami drove in a two-run double in the bottom of the ninth inning as Japan came back from a 5-4 deficit to reach Tuesday’s final in Miami against the USA.
Japan are chasing a record third World Baseball Classic crown after winning the tournament in 2006 and 2009.
The Asian powerhouses have been the most consistent side in this year’s tournament, averaging more than nine runs per game en route to Monday’s semi-final.
But for long periods of a thrilling duel at Miami’s LoanDepot Park it looked as if Mexico were ready to score an upset.
A superb pitching performance from the Los Angeles Angels’ Patrick Sandoval stymied Japan’s vaunted offensive power through the first four innings.
Mexico meanwhile broke the game wide open in the fourth.
After bagging two outs, Japan prodigy Roki Sasaki gave up singles to Rowdy Tellez and Isaac Paredes on successive pitches before Luis Urias blasted a homer to left center-field to put Mexico ahead 3-0.
The Houston Astros’ Jose Urquidy replaced Sandoval in the fifth and navigated a bases-loaded jam to keep Japan scoreless.
Urquidy emerged unscathed from another bases-loaded situation in the sixth to frustrate Japan again.
But Mexico’s resistance finally broke in the bottom of the seventh.
Boston Red Sox new signing Masataka Yoshida smashed a three-run shot to tie it up at 3-3 and Japan were back in it.
Yet Mexico responded well to start the eighth. Randy Arozarena doubled to lead off and then scored when Alex Verdugo doubled.
A Paredes single put Mexico up 5-3 and Japan were again chasing the game.
Hotaka Yamakawa’s sac-fly to left field scored Takumo Nakano to trim the deficit to 5-4 heading to the ninth.
After Mexico went scoreless in the top of the inning it was left to Japan’s golden boy Shohei Ohtani to start the fightback.
Ohtani doubled off Giovanny Gallegos to keep Japan alive and then the pressure piled on the Mexican pitcher as Yoshida walked, and was replaced by pinch-runner Ukyo Shuto.
Murakami then stepped up to crush a double to center field and Ohtani and Shuto sprinted home for a stunning walkoff win.
AFP