Romney, who narrowly beat Rick Santorum in Iowa this week, had the most to lose in the debates as the other Republicans in the race try to prevent him from running away with the nomination.
Santorum, Newt Gingrich and Rick Perry are competing to emerge as the conservative alternative to Romney. Jon Huntsman and Ron Paul are fighting to remain relevant.
Saturday night's debate was the first in more than three weeks, and the first since Michele Bachmann dropped out after the Iowa caucuses.
The candidates are facing a quick turnaround for the second debate, which is set for Sunday morning in Concord.
