Ouattara’s Republican Rally (RDR) was reported to have won 123 of the 255 seats in parliament in Sunday's poll, with the results in 27 seats still to be announced.
The PCDI have taken 93 and independents 12.
Former president Laurent Gbagbo’s Ivorian Popular Front (FPI) boycotted the poll.
The pro-Ouattara press was exultant Wednesday but the victory could mean problems for the RDR’s relations with the PDCI after they failed to form a united front to fight the election.
The PDCI’s support helped Ouattara win the presidency in last year’s election, which was followed by violence as Gbagbo tried to hang onto power, and the party was expected to be given the prime minister’s position.
But the post went to Guillaume Soro, head of the former rebel New Forces movement, who is to meet International Criminal Court prosecutor Luis Moreno-Ocampo in New York on Thursday. Moreno-Ocampo has said that both sides were involved in post-election rights abuses.
Soro was elected in his northern stronghold of Ferkessedougou with nearly 99 per cent of the votes, as was widely predicted.
Map of Côte d'Ivoire
West Africa regional bloc Ecowas said Tuesday that Sunday's election was free and fair but that turnout was low.
Former Haitian prime minister Gérard Latortue, who headed a group of observers from French-speaking countries, advised the FPI not to boycott forthcoming local council elections.
“One principle of representative democracy: the absent are always wrong,” he said on Ivorian television on Tuesday.
Exiled FPI spokesperson Justin Koné Katinan put turnout at 20 per cent, compared to 80 per cent in the presidential election.