Japan's Taguchi smashed Billy Wagner’s pitch to break a ninth-inning tie and Scott Spiezio drove in three runs as the Cardinals rallied for the victory that will send the best-of-seven series to St. Louis tied at one game each.
Cardinals manager Tony La Russa put Taguchi into the game in place of left fielder Chris Duncan after St. Louis already had taken the field in the bottom of the eighth.
It proved an inspired move when Taguchi sent the ninth pitch he saw from Wagner over the left field wall to break a 6-6 tie.
The shot became the second homer in as many at-bats this postseason for Taguchi, who also homered in game three of the first-round series against San Diego.
He had only two homers in 316 at-bats during the regular season, and Wagner had allowed just one home run since August 12.
"Who's expecting that I hit a home run," Taguchi said with a laugh. "Nobody, not even me."
The Cardinals added two more runs off Wagner when Albert Pujols doubled and came home on a two-base hit by Spiezio, who was inserted in the lineup to replace the slumping Scott Rolen.
Albert Pujols gets in the mood
"In any normal situation if Rolen was anywhere near the way he should be I wouldn't start," Spiezio said. "With that situation I still feel it does give me a lot of confidence because Tony ... feels like I can have some big at-bats for him."
Juan Encarnacion capped the inning with an RBI single.
The postponement of Wednesday's series opener by rain allowed La Russa to move up Chris Carpenter to Friday and still work on regular rest.
But the Cardinals' ace was nowhere near his best, allowing five runs, six hits and four walks in five innings.
Delgado belted a three-run homer in the first and added a solo shot in the fifth against Carpenter to give the Mets a 5-4 lead.
Paul Lo Duca's RBI double in the sixth gave New York a two-run cushion.
Delgado breaks drought
Delgado became the first Met with two homers in a postseason game since Edgardo Alfonzo did it against Arizona in a 1999 Division Series.
Jose Reyes was just 2-for-16 in the postseason before doubling to right field against Carpenter in the first inning. Lo Duca sacrificed and Beltran walked to set the stage for Delgado's homer.
An error in the next inning by Delgado allowed the Cardinals to slice the deficit to 3-2.
The veteran first baseman booted a grounder by Spiezio to put runners on second and third. Two batters later, Yadier Molina sliced a two-run double to right field.
Scott Speizio hits the mark
Reyes made it 4-2 with an RBI single in the bottom of second to score Endy Chavez, who reached on a leadoff double. Chavez started in left field in place of Cliff Floyd, who aggravated an Achilles tendon injury on Thursday.
Mets rookie hurler John Maine quickly gave the lead back, however, allowing an opposite-field two-run homer to Edmonds in the third that tied the game at 4-4.
Main allowed four runs - three earned - two hits and five walks five before being lifted for a pinch hitter in the fourth.
"We've had bigger challenges than this," said Mets manager Willie Randolph. "We always respond. We've responded all year, and I don't think it's going to change now."