European Union officials said that a key step in clinching a deal was getting China and major emerging economies to commit to language on trade early this week.
"The idea was to bring the Chinese into the discussion almost immediately," said a second European official. "After APEC, we knew it would be important for the Chinese to feel there was no ganging up on them."
At the Asia-Pacific Economic Cooperation (APEC) summit in mid-November, leaders failed to agree on a joint communique for the first time in the group's 30-year history.
After APEC, Washington and Beijing traded accusations of blame but, with global markets increasingly roiled by trade tensions, both sides appeared more ready for compromise in Buenos Aires.
After the G20 talks ended, Trump and his Chinese counterpart Xi Jinping agreed over dinner on Saturday to a ceasefire in their trade conflict, calling off higher U.S. tariffs that were to go into effect on Jan. 1.
"The spirit wasn't adversarial," said the delegate closely involved in the G20 drafting, adding that perhaps because of the fallout after APEC, officials at least tried to work things out.
Delegates worked until 6:30 a.m. on Saturday, the final day of the summit, watering down language on migration and refugees in the face of resistance from the United States and others, European and Argentine officials said.
And they still had not tackled one of the thorniest issues: climate change.
"That was what they discussed (Saturday) morning till noon," an Argentine government spokeswoman said, just hours before the communique was made public.
In the end, members agreed to disagree. The United States reaffirmed its commitment to withdraw from the Paris Climate Accord - as it had at the previous G20 summit in Germany last year - while other members said they would fully implement it.
Veteran negotiators were phlegmatic about the difficulties in agreeing on a text.
"There is always at least one overnighter in sessions like these," said the delegate closely involved in the drafting, adding "sometimes it was tough to find the right word to stick to the middle ground."
