Pakistan Muslim League-Nawaz, the party of the former prime minister Nawaz Sharif, had rejected the incomplete results, but by Friday conceded defeat to Imran Khan's Pakistan Tehreek-e-Insaf party.
Pakistan's former ruling party conceded the country's election to cricket star legend-turned- politician Imran Khan as final results were expected on Friday, paving the way for Khan to begin searching for coalition partners.
Khan, during a speech declaring victory on Thursday, offered to investigate opposition claims of vote rigging and vowed to improve relations with neighbours India and Afghanistan, while calling for "mutually beneficial" ties with the United States.
The party of jailed ex-prime minister Nawaz Sharif initially rejected the so far incomplete results, but by Friday its leaders appeared to accept that Khan would be the next prime minister.
TRT World's Kamran Yousaf brings the latest from Pakistan's capital Islamabad.
'Will sit on opposition benches'
"We are going to sit on opposition benches, despite all the reservations," said Hamza Shehbaz Sharif, a parliamentarian and the nephew of Nawaz Sharif, who is in prison after being convicted on corruption charges he disputes.
The allegations of rigging in Wednesday's election followed a bitter campaign in which Pakistan's powerful military was accused of tilting the race in favour of Khan, and trying to erase democratic gains made since the most recent spell of military rule ended in 2008.
Although Khan appeared likely to fall short of the 137 seats needed for a majority in the National Assembly, his better-than-expected results mean he should have no problems forming a government with a handful of small coalition partners.
One of the first tasks for Khan, once he forms the government, will be to avert a currency crisis, which follows four devaluations of the rupee currency since December, and will likely require Islamabad to seek Pakistan's second International Monetary Fund bailout since 2013.
The latest Election Commission of Pakistan (ECP) official partial results showed Khan's Pakistan Tehreek-e-Insaf (PTI), or Pakistan Movement for Justice party, had won 115 seats out of the total of 272 National Assembly seats.
Sharif's Pakistan Muslim League-Nawaz (PML-N) had 62 seats, the results showed. The Pakistan Peoples Party (PPP), led by Bilawal Bhutto Zardari, the son of assassinated two-time prime minister Benazir Bhutto, was third with 43 seats.
"(PML-N) would play the role of a strong opposition," said Shehbaz Sharif, the PML-N president and brother of Nawaz Sharif, according to the English-language Dawn newspaper.
Who will rule Punjab?
Khan's party also appears to have succeeded in wresting control of the local assembly in Pakistan's biggest province, Punjab, from the Sharifs.
The News newspaper and other local media reported PML-N was unlikely to form the government in Punjab, home to more than half of Pakistan's 208 million people and the power base of the Sharif family for more than three decades.
Shehbaz Sharif has said the vote count was rigged and vowed to offer evidence to the ECP.
Both the PML-N and PPP say their party monitors at many voting centres were either kicked out during counting or had not received the official notifications of the precinct's results, instead being given handwritten tallies they could not verify.
Pakistan's election monitoring body and a team from the European Union were scheduled to deliver their assessments of the conduct of the election on Friday.
Nearly finalised results also indicate religious parties that fielded more candidates than ever before failed to win any National Assembly seats.
The Allahu Akbar Tehreek party of Hafiz Saeed, who is accused of masterminding the 2008 attacks that killed 166 people in the Indian city of Mumbai, did not win a single seat. Neither did candidates linked to Sunni extremist group Ahl-e-Sunnat Wal Jamaat.
Tehreek-e-Labaik Pakistan, which campaigns under the rallying cry "Death to Blasphemers" also failed to win any seats, although results indicate it garnered a large following across Punjab.