Sabahy has had the backing of many who supported the Cairo's Tahrir Square uprising last year to protest Mubarak's rule. Sabahy is a proponent of late and revered Egyptian leader Gamal Abdel Nasser, who ruled the country in the '50s and '60s.
Elgindy said it is hard to predict where the votes of liberals and revolutionaries will go if they do participate, but the Muslim Brotherhood will have to work hard if it wants to win them over, having alienated many in the past. Many people may opt to stay at home rather than make a "very difficult choice" in the runoff, Elgindy said.
There is also a chance of further protests and even violence regardless of who wins, Elgindy said, as revolutionary elements become increasingly marginalized and radicalized.
Mubarak led the North African nation for 30 years before being forced out last year amid a popular outcry.
The voting is a monumental achievement for those who worked to topple Mubarak in one of the seminal developments of the Arab Spring. And it could reverberate far beyond the country's borders, since Egypt is in many ways the center of gravity of the Arab world.
Distrust and anger in Egypt, particularly against the military's power in governmental affairs, have inspired continued protests, some of which have been marked by deadly clashes. Many protesters are upset about what they see as the slow pace of reform since Mubarak's ouster. Some are also concerned that the country's military leadership is delaying the transition to civilian rule.
Worries about the powerful military possibly swaying this week's vote persist despite the insistence of the Supreme Council of the Armed Forces that it will hand over power to an elected civilian government.
The military leaders put armored personnel carriers on the streets with loudspeakers broadcasting a message that they will relinquish power, but that did not convince doubters.
In January, two Islamist parties -- the Freedom and Justice Party with 235 seats and the conservative Al Nour party with 121 seats -- won about 70% of the seats in the lower house of parliament in the first elections for an elected governing body in the post-Mubarak era. The rest of the assembly's 498 seats were divided among other parties.