Cardinals 4, Cubs 3 (12). St. Louis began the game with Adam Wainwright, who has twice finished second in Cy Young voting and owns a career ERA+ of 131. Chicago opposed him with Jake Arrieta, who has never entered a Cy Young voter's mind and has a career ERA+ 50 points lower. That's... about right, for these two teams.
The pitchers got off to similar starts - each allowed a fruitless one-out single in the first (to Luis Valbuena and Jhonny Peralta, respectively), and both let a runner reach third with two out in the second (Wainwright on a Nate Schierholtz walk, a Welington Castillo single, and a forceout; Arrieta on a Peter Bourjos double, an intentional walk to Mark Ellis, and an embarrassing unintentional walk to Wainwright) before stranding them.
The Cubs jumped out to the game's first lead in the top of the third when Arrieta singled and Valbuena homered. The Cardinals threatened in the bottom of the inning, starting with walks by Peralta and Matt Holliday. One out later, Yadier Molina singled, with Peralta getting thrown out at home on the play; Matt Adams would go on to single in one run, but there could easily have been more.
Both starters stranded a sole baserunner in the fourth, and Wainwright did it again in the fifth. The bottom of the inning began with Arrieta being pulled for Carlos Villanueva, who allowed an Allen Craig double but left him at third. In the sixth, Castillo joined Schierholtz and Emilio Bonifacio on the list of Cubs to single and get left on in the middle innings.
Bourjos reached on a bunt single to start the bottom of the sixth, and moved to second on a groundout. Jon Jay hit for Wainwright and walked, with Bourjos adding insult to injury by stealing third on ball 4. Wesley Wright took over for Villanueva and induced a grounder to short from Matt Carpenter, but Starlin Castro made a throwing error on the play, resulting in all runners being safe and the tying run scoring. Peralta followed with a go-ahead RBI single. Wright stranded the remaining pair of runners, but the Cubs were now trailing for the first time in the game.
The Cardinal bullpen promptly went to work securing the newfound lead. In the seventh, Kevin Siegrist walked Mike Olt, then benefited from a K/CS double play courtesy of Olt and Bonifacio. After Neil Ramirez escaped the bottom of the inning courtesy of a conventional DP, Siegrist notched the first out of the eighth, then walked Anthony Rizzo; Carlos Martinez relieved and retired the next two Cubs. (Martinez joined the game as part of a double switch, with Adams coming out, Craig moving from right to first, and Joey Butler taking right and the ninth spot in the order.) Chicago also double-switched in the bottom of the inning, amid Ramirez and James Russell putting the Redbirds down 1-2-3; Schierholtz was replaced by Chris Coghlan in right.
Trevor Rosenthal came on for the save chance in the ninth and started by getting Castillo to line out. Junior Lake then singled, and Darwin Barney walked, putting the tying run in scoring position. Coghlan struck out looking, but Bonifacio singled to even the score at 3. Russell threw a spotless ninth to send the game into double digit innings.
The extra session started out relatively dully. Rizzo drew a leadoff walk from Sam Freeman in the tenth, but was caught stealing while Castro struck out, because apparently the Cubs hadn't learned the pitfalls of sending slow corner infielders against Yadier Molina when they tried it earlier in the game. Brian Schlitter threw perfect tenth and eleventh innings, and Pat Neshek matched his effort in the latter. Seth Maness finally allowed another runner in the twelfth when Valbuena doubled, but after an intentional pass to Rizzo, Castro grounded out to leave the go-ahead run in scoring position.
Justin Grimm relieved in the bottom of the inning and allowed a leadoff hit to Peralta; after Holliday fouled out, Grimm decided to start pitching as though the strike zone had been abolished, walking both Craig and Molina and then hitting pinch hitter Greg Garcia with a pitch to force in the winning run.
This game had an unusual scoring pattern - one or more runs came in every three innings, but not in between. It also included a starting pitcher getting removed after 4 well-pitched innings without having an absurd pitch count (82). Further, it went 12 innings and had a game-tying rally in the ninth.
But mostly, the game had a walkoff HBP - and not just any walkoff HBP, but one that represented the batter's first career RBI. I feel fairly comfortable guessing that this is a less-than-common event.