The DA can take sole control of the Western Cape government after winning an outright majority in the province with more than 51 percent of votes.
The Independent Electoral Commission said early on Saturday that the party had taken 51.46 percent of the vote, nearly double its tally in 2004 and a resounding victory over the ANC whose vote share fell sharply to 31.55 percent.
"Yes, the DA won an outright majority," IEC communications manager Trevor Davids said, but added that the results had yet to be formally declared.
It is the first time since the end of apartheid that a party has scored an overall majority in the province and the result of a driven campaign by DA leader Helen Zille to unseat the ANC.
COPE won 7,74 percent of votes and knocked the Independent Democrats into third place in the province. The ID slipped from seven percent five years ago to 4,68 percent.
Zille has promised supporters that as the new premier of the Western Cape she will serve the interests of all people in the province, where racial divides run deep.
"We will try to govern as well as we can to show that life is better for everybody under the DA," Zille said late on Friday after arriving at Cape Town airport to a hero's welcome.
Although the election result means that the DA does not need coalition partners in the provincial legislature, Zille has hinted that she might still form an alliance with smaller parties.
She will be taking control of the province after receiving good reviews of her three-year stint as mayor of Cape Town, which boosted the DA's campaign in the hotly contested province.
The ANC, on the other hand, has been weakened by leadership problems in the province, where it took 46 percent of votes in 2004.
The Western Cape is the only region where the opposition has managed to wrest power from the ANC in this week's elections.
Early on Saturday the DA was lying at 20 percent in Gauteng, while the ANC had victory firmly in hand with more than 64 percent of the vote in the province.
Zille has charged that a constitutional amendment approved by the cabinet on the eve of the elections was a blatant attempt by the ANC to limit the powers of local governments, particularly those under control of the opposition. - Sapa