Many whooped and cheered.
Romney's sons took to Twitter to celebrate their father's performance. "Now that was fun," wrote Tagg Romney, the eldest.
Tagg then retweeted his brother, Josh.
"Clear eyes, full hearts, can't lose," Josh wrote.
The phrase comes from the TV series "Friday Night Lights." A picture attached to Josh's tweet showed Mitt and Ann Romney underneath a sign with that phrase printed on it and overlaid on the "R'' Romney logo.
Romney spent much of debate day surrounded by his family. In the morning, he took time to meet with top advisers to finish debate preparation. But after he returned from a visit to the debate hall in the afternoon, four of his five sons joined him in his hotel room, along with wife Ann and two of his grandchildren.
He and Ann had a takeout dinner from The Cheesecake Factory — he had spaghetti and a barbecue sandwich.
Even before the debate began, the Romneys huddled together as a family. Mitt and Ann Romney watched their sons play Jenga, a game of stacked wooden pieces where players pull them out one at a time until the wooden tower falls.
Sons Craig and Matt Romney were shown in photos playing with Nick, who is Matt's son and Mitt's grandson.
Also before the debate, Obama got a visit from his wife, Michelle, who arrived in Denver on Wednesday afternoon following a solo campaign swing. The two rode to the debate together in the president's black armored limousine, eliciting cheers from a crowd gathered outside Obama's hotel on the first couple's 20th wedding anniversary.
Copyright 2012 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.