But that effort seemed to run aground, as two former candidates, Amr Moussa and Abdel Moneim Aboul Fotouh, released statements saying they were not endorsing Mr. Morsi or any candidate, though they did not say whether that would change.

And Mr. Sabahi, whose supporters are coveted by both remaining candidates, seemed to be trying to keep his own campaign alive on Saturday. A lawyer representing him told Reuters that the campaign had appealed to the presidential election commission to halt the runoff for reasons that include allegations of “irregularities” during the first round of voting.

At a rally at his campaign headquarters on Saturday night, Mr. Sabahi told throngs of cheering supporters that he would not endorse another candidate, or accept an offer to serve as vice president. “Sabahi is our president!” the crowd roared. “We will never abandon him.” Also on Saturday, former President Jimmy Carter, who led a delegation that monitored the first round of the elections, said there were “many violations” but added that they did not “violate the integrity of the elections as a whole.”

Speaking in Cairo, Mr. Carter said restrictions placed on his organization by the Egyptian authorities were the strictest the group had faced in 25 years, and as a result it was not able to certify the process as “proper.”

He added, “The Egyptian people have accepted the process we have seen over the last few days as quite successful.”

Even so, many Egyptians threw up their hands at the results. Some argued that the outcome was inevitable: that an electorate battered by a chaotic transition and under temporary military rule would easily reach for candidates who appealed to fear rather than hope.