(Reuters) - When Kevin Durant joined the Golden State Warriors many felt a championship was a mere formality, but a humbling season-opening loss has sent a sudden wakeup call to one of the NBA's most talented teams of all time.

Durant had a team-high 27 points in his much anticipated Warriors debut on Tuesday but Golden State stumbled to a 129-100 blowout loss to the visiting San Antonio Spurs that prompted many in the sellout crowd to head for the exits early.

"It's a slap in the face. It woke us up a bit, and we're looking forward to getting better," four-time scoring champion Durant told reporters.

Durant was one of the most sought-after free agents in years and his decision to join the Warriors in July formed one of the most impressive collections of talent the NBA has seen.

But it was not the start anyone could have imagined, especially for a Warriors team that opened last season with a stellar 24-0 run en route to a record-setting 73-9 campaign. That run also saw them win their first 36 home games.

"It's a nice little slap in the face," two-time reigning NBA Most Valuable Player Stephen Curry said.

"First game you want to come out and protect your home court and have the energy of the home opener live throughout the game. We didn't do anything to let that happen."

While the season-opening loss will not define the Warriors' campaign, it was enough to showcase some areas they will need to address if they are to live up to the lofty expectations heaped upon them.

But while the Spurs, no slouch of a team having finished with the league's second-best record last season, took advantage of the Warriors' weak defense, rebounding, turnovers and bench production, even they were somewhat stunned by the result.

"If there was an outcome I wasn't expecting, it was this one," Spurs guard Manu Ginobili said. "A 29-point lead against a team like them? I truly didn't expect it."

The Warriors, whose bid to repeat as NBA champions fell one game short after they squandered a 3-1 series lead in the NBA Finals to the Cleveland Cavaliers in June, will try to regroup in time for Friday's game at the New Orleans Pelicans.

"What we can't do is let these games pile up," said Durant. "We can't panic. It's Game 1 of 82."

(Reporting by Frank Pingue in Toronto; Editing by Mark Lamport-Stokes)