The Cubs, having contended briefly in 1927 and 1928, got off to a decent start in 1929 and then roared through July and August with a 44-18 record, including an eight-game winning streak. That put them 11½ games ahead of the second-place Pirates beginning September, when they would host the Cardinals in a three-game series. That consisted of a single game on the first day of the month and a doubleheader on Labor Day, September 2. (The image at the top of this post is the scorecard that patrons would have seen at Wrigley that year; you'll be seeing many similar scorecards as this series continues.)
In those days -- the present imitating the past in some ways -- doubleheaders were played as split-admission affairs, the first game in the morning, then after the ballpark was cleared, the second game in the afternoon. And so, our "Game" is actually two, again, for the 1929 entry in this series.
The Cubs won the first game of the series 10-3; the first game of the doubleheader drew 38,000 fans for an 11-7 Cubs win, and the second game completed the sweep, 12-10, in front of 43,000. (Both of those numbers were estimates; no exact attendance mark for those games exists.) Remember that Wrigley didn't have the current bleacher configuration at the time, and also had non-permanent seats; they could and often did squeeze crowds of 45,000+ into the ballyard. The season attendance of 1,485,166 was almost double the amount that the team with the second-biggest crowds had (Giants, 868,806); it set a club record that was not broken for 40 years, until 1969.
Edward Burns of the Tribune picks up the story of the sweep over St. Louis:
So much happened during the exercises that the panorama is likely to become somewhat blurred unless you concentrate like everything. So, what do you say we gather around and calmly summarize some of the outstanding features. The crowd at the morning game broke all records for preluncheon contests in the history of baseball and the total attendance of 81,OOO has been surpassed only in the Yankee stadium and otherwise never approached here or elsewhere. Rogers Hornsby knocked his 31st home run in the morning game and his 32d in the afternoon game, the first with one on and the second with two on. Hack Wilson rapped out his 35th homer of the season in the morning game. Kiki Cuyler stole his 34th base in the morning game. Pat Malone, in winning the morning game, hung up his nineteenth victory of the year, which makes his total more than anyone in the National league. Though Pat was touched up freely, he also had his strikeout ball working, mowing down no fewer than eight.
Those numbers should give you a pretty good clue as to why the Cubs were pennant winners in 1929; they led the league in runs scored (982; next best was the Pirates at 904), and allowed the second-fewest (756, to the Giants' 706). Hornsby, a future Hall of Famer acquired in a massive deal in November 1928 (five players plus $200,000 went to the Braves in exchange), won the N.L. MVP award by hitting .380/.459/.679 with 39 home runs, 149 RBI and 156 runs scored. That runs total is still the club record; the only player in the last 83 years to come close to that was Sammy Sosa in 2001 (146).
The Cubs won the pennant by 12½ games, but it wasn't enough to win the World Series, after A's manager Connie Mack had sent Howard Ehmke, a 35-year-old pitcher thought to be near the end of his career, to scout the Cubs late in the season. He then started Ehmke in Game 1, shocking the baseball world; but Mack's hunch proved right. Ehmke struck out 13, which stood as the World Series single-game record until 1953. Later in that World Series, the Cubs had an 8-0 lead in the seventh inning of Game 4; they were that close to tying the series, but the Athletics put up a 10-run inning and put the Cubs away in five games.
Cubs history is filled with stories like that. Unfortunately.