The Mitsubishi driver, who won the event on a bike in 2004 before switching to four wheels, was only sixth in stage three but moved to the top of the leaderboard.
"I am very surprised and happy to be leading," said Roma. "I just tried to reach the finish without any mistakes. It is dangerous to push in the dust. At one point there were 10 or 15 bikes together."
The competitors made the trip from Europe by boat overnight before beginning the first African stage in Nador, travelling south 417 miles to the Moroccan town of Er Rachidia.
Former world rally champion Carlos Sainz had held the overall lead after two stage wins in Europe but his inexperience on the African sand hindered him. The Spaniard, in his first Dakar Rally, slipped to fourth overall.
Frenchman Jean-Louis Schlesser, driving a Ford-powered buggy, took the stage honours, beating Hiroshi Masuoka, in a Mitsubishi, by 19 seconds. Masuoka's time lifted him into second place overall, just six seconds behind Roma. Volkswagen's Bruno Saby lies third. Reigning champion Stephane Peterhansel, clocked the third fastest time and moved into sixth overall for Mitsubishi.
He confessed he had not pushed flat out, preferring to take it easy until the later stages of the 5,500-mile contest.
In the bike class, Cyril Despres is well placed to defend the crown he won last year after moving into the overall lead. Despres moved to the top after previous leader Isidre Esteve Pujol conceded 11 minutes to slide to ninth.Reuse content