The results had been due by around 2 a.m. (2100 GMT on Wednesday).
The elections are being held as emotions run over a graft case that led to the imprisonment of ousted Prime Minister Nawaz Sharif and his daughter Maryam Nawaz. The provincial results show that the PML-N was leading on 129 seats in Punjab followed by PTI with 121 in the provincial assembly of 299 members.
It appears likely that Tehreek-e-Insaf will fall short of the 137 seats needed to form a government, raising the prospect Mr Khan's party will have to find coalition partners.
Khan called for "mutually beneficial" ties with Pakistan's on-off ally the United States, and offered an olive branch to arch-foe India, saying the two nations should resolve the long-simmering dispute over Kashmir.
Bhutto - son of slain prime minister Benazir Bhutto - and his PPP could be called upon to form a coalition with any victor.
Before official results arrived, PTI and Khan supporters took to the streets to celebrate the initial results on Wednesday night. During the campaign, reports emerged that such pressure had prompted dozens of Muslim League candidates or rising figures to leave the party.
Khan has been an outspoken critic of the USA -led war in neighbouring Afghanistan as well as China's massive investment in Pakistan, which has racked up millions of dollars in debt to Beijing.
Khan has also criticized Pakistani liberals and embraced conservative Islam as a politician, promising a Taliban-style justice system.
Pakistan Election 2018: 53,000 observers will monitor polls
Recent polls show PTI's popularity climbing nationally. "I am supporting Imran Khan because he is the best choice for Pakistan". BehindYouSkipper became one of the country's top trending hashtags as celebrities and former cricketers came to Khan's support.
He is also widely believed to be backed by the army, which fell out with Nawaz Sharif, who looked to curb the military's traditional dominance in politics.
Monitors had been thrown out of polling stations as votes were tallied and results were unexpectedly delayed for hours.
"I say to the people of this country today, we will govern Pakistan like it has never been governed before". "Why don't you think the five political parties might be wrong?"
"Claims of electing rigging occur after every election in Pakistan - but this time around, they will be harder to brush aside given the overt role the military has played", said Shamila Chaudhary, a former White House and State Department official who's now a fellow at Johns Hopkins University School of Advanced International Studies. The Pakistan Peoples Party was leading on 44 seats while others were ahead in 17 seats.
Pakistan went to polls on July 25 in the nation's second democratic transition of power ever in 70 years. Final results are expected early Thursday. As many as 11,673 candidates are contesting the elections from across the country.
Under Pakistani law, separate seats are reserved for women and for non-Muslim minorities, who comprise 4 percent of the population.
As voting ended, festive supporters of both parties gathered outside polling stations, dancing to the beat of drums.
Sharif, 68, was removed by presidential decree in 1993, in a military coup in 1999, and past year by the Supreme Court, which ordered his corruption trial.