The home run capped off a six-run comeback which started in the seventh. The Pirates came into the bottom of the inning down 9-3, and managed to make it a 10-6 heading into the ninth.
That's when things started to get crazy.
Michaels and Jack Wilson reached base to begin the ninth, and Nate McLouth brought them home with a deep blast to right-center field to make it 10-9.
Then, with runners on the corners with one out, Jason Bay sent a dribbler to short. But middle infielders Cesar Izturis and Aaron Miles were unable to complete the double play and Luis Rivas scored to tie the game at 10.
Troy Glaus appeared to have ended the Pirates' hopes in the top of the 10th with a solo home run to left field, but Michaels answered the Cardinals third baseman with a two-run shot to win the game.
"That was one of the more amazing games I've ever been involved in," Bay said. "That was something I'll never forget."
"They kept after it," manager John Russell said. "It looked like we were well out of reach. We kept pecking away. I think the biggest thing is these guys never quit. They always battle. They pull for each other. It's been phenomenal."
The comeback overshadowed Yoslan Herrera's rough Major League debut. The Pittsburgh right-hander's unorthodox, toe-tapping delivery seemed to be too confusing for the Cardinals at first, as he struck out Cardinals sluggers Albert Pujols and Rick Ankiel in succession to end the first inning.
Herrera's Houdini act in the second was even more impressive. After loading the bases with no one out, Herrera got a pop out before inducing second baseman Adam Kennedy into an inning-ending double play.
But that's when Herrera's luck finally ran out. The Cardinals ended up scoring six runs off Herrera over the next three innings. In total, the rookie gave up 11 hits, four walks but struck out four in 4 1/3 innings.
"I thought he was OK," Russell said. "He throws a lot of offspeed stuff, so he's got to use his fastball to really set that up. I thought occasionally he went too soft, too often and they made the adjustment on him. I think he's got good stuff. I was very intrigued by what I saw."
The barrage was part of a 22-hit attack -- the most hits in a game by the Cardinals this season.
Jason Bay gave the Pirates an early 2-0 lead in the first on a home run to right-center field. Bay's blast, his 18th of the season, tied him with Al Oliver for 10th place on the Pirates' all-time home run list. Bay then passed Oliver with another two-run homer in the eighth to pull the Pirates within four.
The Pirates left fielder now has 51 RBIs this season to go along with 19 home runs. He is now one home run short of tying Kevin Young (136) for ninth place on the all-time list.
Doug Mientkiewicz was thrown out of the game in the fourth after a play he helped create. Pujols hit a line drive that caromed of Mientkiewicz's glove toward the tarp along the baseline. Pujols took a hard turn around first and appeared to be tagged out by Luis Rivas at second, but umpire Eric Cooper called the Cardinals first baseman safe.
Television replays showed that Rivas applied the tag to Pujols' right shoulder before he touched the base. Mientkiewicz was ejected moments later for arguing the call.
McLouth kept the Cardinals from scoring more than two runs in the sixth with a pretty diving catch in right-center field. McLouth then got up and threw a dart to LaRoche at first to double up Troy Glaus.