Teams worked through the night "changing the text" and "got a lot of work done", Guajardo said.
Guajardo stressed that the most hard issues had been left to the end, including the USA demand that NAFTA be approved every 5 years, a provision known as a sunset clause.
Before entering the meeting with Lighthizer, Guajardo was asked by reporters whether Canada would take part next week in the talks, and he said "possibly".
He added that any deal with Mexico must take care of American autoworkers and farmers, but he praised the new Mexican president, calling him "an absolute gentleman".
Speaking as he left a meeting with the US trade team in Washington, Ildefonso Guajardo said the return of Canada, the third country in the trillion dollar trade zone, would depend on solving bilateral elements in "the next few days or weeks". He says the country's "Tariffs and Trade Barriers are far too high" and is threatening to "tax cars if we can't make a deal!"
Foreign Minister Luis Videgaray, who accompanied Guajardo, spoke to US Secretary of State Mike Pompeo on Wednesday and "discussed the importance of concluding a NAFTA agreement", according to a statement from the State Department.
Trump demanded NAFTA be renegotiated after repeatedly criticizing the 24-year-old pact as a "terrible deal".