Del Rosario, 72, won a gaping margin of at least 46,000 votes over Gementiza in both districts of the province after garnering 84,157 votes.
Gementiza, who is seeking for a second term, conceded defeat a day after counting began when he was trailing behind Del Rosario by the thousands.
Namfrel has released its final unofficial tally from vote-rich Tagum City, the provincial center, and the man who helped build the giant banana exporter Tagum Agricultural Development Corporation (Tadeco) enjoyed a relatively wide margin over Gementiza in an area known to be a bailiwick of the 74-year-old politician.
According to Namfrel, Tagum City gave Del Rosario 39,754 votes while Gementiza, more known popularly as Yayong, got 27,227.
It was believed the second district gave the former secretary of new government centers the wide margin since the known turf of the Del Rosarios and the sprawling Tadeco are in the same district.
Areas with considerable number of voters are in the cities of Panabo and Samal.
"As we see in the results, Gov. Del Rosario is winning. I congratulate him," Gementiza told reporters.
He called on everyone, including his supporters, to back whatever programs his successor implements.
In Tagum City, Mayor Rey Uy is poised for another three-year term as Lakas-CMD bets dominated opposition candidates 12-0, from the mayoralty seat down to the city council.
The last-termer city executive enjoyed a 39,723-vote margin against opponent Meliton Lemos, a police officer-turned lawyer, who previously served as a senior member of the provincial board representing the first district.
Uy has 58,294 votes while Lemos got 18,571.
Another Uy, the mayor's son De Carlo, shot to number three in his first bid for the city council, earning about 43,000 votes.
The younger Uy was a neophyte in local politics, his name surfaced only during the election period.
Many believe the overwhelming support of the Tagum electorates for his father benefited De Carlo.
Another Gementiza, son of the outgoing governor, suffered the same fate as his father. Geterito "Boyet" Gementiza lost to incumbent Allan Rellon for the vice mayoralty race. Rellon got 44,893 votes while Gementiza has 28,633.
In the congressional race for the first district, incumbent Rep. Arrel Olaño was ahead with 48,054 votes as compared to former Transportation Secretary Pantaleon Alvarez, who got 39,265 votes.
According to Namfrel, chaired by Rev. Father Ben Cañete of the Tagum diocese, the results did not include election returns that did not arrive from barangays Magugpo South, Visayan Village, Apokon, Madaum, San Agustin and San Isidro.
Namfrel said the ERs were supposed to come from 13 polling precincts in these areas.