Can you do this without an extension? SURE, but this saves some steps!
Tab Glue puts the two pages back together. Or if you have two Chrome windows open, tab glue with put them together.
Find them at the Chrome store here: Tab Scissors and Glue
NiftySplit takes the same concept a bit further. With Nifty Split installed, you can right click on any link on a webpage, and the option "Open as NiftySplit Window" appears. Selecting that will split the screen with two windows - the link you right-clicked will appear in the right window, and the existing page will remain on the left. Where it gets fancy is that when you navigate in the window on the left side, any link you left click on while in NiftySplit mode will open in the right screen, so you can consistently change what appears on the right screen. Hitting Shift click will open a link in the left window. Play around with it, and you will see what happens. Pretty nifty!
Find NiftySplit at the Chrome store here: NiftySplit