The 25-year-old Hernandez hit .190 with seven homers and 18 RBIs in 109 games this year. He went 2 for 24 with 12 strikeouts over his last 10 regular-season games and was not active in the Division Series against Washington.
Dodgers manager Dave Roberts said he likes Hernandez's athleticism and versatility. His addition to the lineup gave Los Angeles another right-handed batter against Cubs lefty Jon Lester in the opener.
''It was a tough decision with Charlie, but I think to have Kike, to get him to start tonight at second base, I think it could pay huge benefits for us,'' Roberts said.
Los Angeles also decided to go with two catchers after carrying three in the Division Series against Washington. Chicago stayed with three catchers.
The major change for the Cubs was the addition of rookie left-hander Rob Zastryzny. Chicago infielder Tommy La Stella was left off the roster.
Zastryzny went 1-0 with a 1.13 ERA in eight games this year, including 3 2/3 scoreless innings at Dodger Stadium on Aug. 27.
''Very high level of confidence in Rob Z,'' manager Joe Maddon said. ''I'm certain that when he goes out there, whenever we do put him out there, there might be a little bit of nervousness within the first two pitches, which I absolutely would want him to be, but after that I think he's the kind of guy that would settle in rather quickly. He's got good makeup. He's solid.''
The move puts four left-handers in the Cubs' bullpen. The Dodgers hit .213 against lefty pitching this year.
This story has been corrected to show Alex Wood is a left-hander.