The strike over unpaid players' wages delayed the start to the lucrative Liga—the first delay to the season in 27 years—and now clubs are trying to stop the action spreading to a second match day.
Players' and clubs' representatives broke off 12 hours of talks in the early morning, citing exhaustion, and were meeting again Thursday morning in the hope of snapping the deadlock.
"The important thing is that we have been here bringing the positions closer together," said the president of the Professional Football League (LFP), Jose Luis Astiazaran.
"I hope we will be able to cancel this strike, if we have the capacity and opportunity to reach a deal," he said.
A visibly tired Astiazaran, whose LFP represents the clubs, said the two sides had advanced in the overnight talks but had decided to take a rest before resuming.
"I am fairly optimistic that tomorrow we will carry on working and try to reach an agreement," he said.
Players, too, reported progress.
"We have been working many hours and those hours have led to advances," Luis Gil, spokesman of the Association of Spanish Footballers (AFE), told reporters as he emerged from the talks before dawn.
"I think we are working very hard. We will be here as many hours as it takes."
Players in the first and second divisions—including stars such as Lionel Messi and Cristiano Ronaldo—went on strike on the first match day last Saturday.
The AFE says 200 players in the top two divisions are owed a total of about 50 million euros ($72 million) in unpaid wages from cash-strapped clubs, some of which are in bankruptcy protection.
The AFE is demanding a wage guarantee and an agreement that players be allowed to break their contracts if they are not paid for three consecutive months, a proposal rejected by the league.