1955 was the year that Ernie Banks burst on the national scene with his first big season; he hit .295/.345/.596 with 44 home runs, 117 RBI, and finished third in National League MVP voting. He set a NL record with five grand slams -- that one still stands.
Unfortunately, that didn't last; they lost 15 of their next 16 to drop well under .500.
Nevertheless, Banks continued to hit, and on August 4 at Wrigley he had the first three-homer game of his career, helping lead the Cubs to an 11-10 win over the Pirates. Irving Vaughn has the story from the Tribune:
As can be judged by the score it was a one hundred percent daffy baseball display in which the Chicagoans went behind in the eighth after once riding high with a 9 to 2 lead. Banks began his day's operations with No. 34 in the first inning off Lino Dinoso, the blow making up for two runs peeled from Howie Pollet's left hand throwing in the enemy opener. The Cubs went on to blast Max Surkont and Dick Littlefield. Banks rested up a bit in the third by confining himself to a single and then took a big hand in a four run fourth. He clouted No. 35 off Surkont with two aboard. A popup stopped him in the sixth and when he showed up again in the eighth Jim King had just been walked by Littlefield and the Pirates were up 1O to 9. He knocked the first pitch into the fenced off section of the bleachers in center.
Banks wound up 4-for-5 that day with four runs scored and seven RBI; it was games like this that helped turn him into "Mr. Cub" -- remember, he was in just his second full major-league season and only 24 years old at the time. The win was the second of six straight that brought the Cubs to within a game of .500, but they never did make it back to even. Still, the 72-81 season was a significant improvement over 1954.
Here's the 1955 scorecard; click on it to open a larger version in a new browser window or tab.