"It's not impossible to beat this Barca side," says Kempes, now 57 and living in Connecticut. "Nothing is impossible in football, but it's very, very difficult. They really know how to play because so many of them have played together for so long and share the same philosophy. They're the best team in the world without doubt. When they play well they always have the ball. If you can't get the ball then you can't score a goal..."
Powerful and aggressive as a player, Kempes knows all about scoring. He bagged six in the '78 World Cup finals for which he was rewarded with the Golden Boot and the South American Player of the Year award - despite being the only foreign-based player among Argentina's World Cup winners. Kempes had moved to Valencia in 1976 from Rosario Central.
Called 'El Matador' by Valencia fans, Kempes was a huge star in Spain. He was La Liga's top scorer in 1977 and 1978 and tasted cup success as Valencia defeated Arsenal in the 1980 Cup Winners' Cup final. Valencia also won the Copa del Rey and the European Super Cup.
He is still loved for his contribution for Los Che and gets mobbed when he goes back - as he does in Argentina - but he didn't bathe in the glory of his international and domestic honours after retiring.
"I was almost like a gypsy," he said of management stints which took him to football outposts like Indonesia, Albania, Bolivia and Venezuela, before managing tiny teams in Spain and Italy. "I love to travel."
Kempes didn't excel in management, but he came 23rd in South America's Player of the Century award. Pele, Diego Maradona, Alfredo Di Stefano and Garrincha occupied the top four places, with Kempes finishing above greats like Ronaldo, Romario and Enzo Francescoli.
Fans admired him throughout Latin America and despite being aggressive and renowned for his surging runs, he didn't pick up a single booking in 43 international caps.
Kempes follows Spanish football closely, but only has eyes for one team.
"Valencia, only Valencia," he says. "The club have had financial problems in recent years and had to sell players like David Silva and David Villa, but I like some of the new signings."
Coach Unai Emery has overseen the captures of goalkeeper Diego Alves from Almeria, midfielder Daniel Parejo from Getafe and French international centre-half Adil Rami from Lille.
"They are young and the competition will help them grow," said Kempes. "Parejo also seems like a good player. He's skilful and has worked well in the teams he has been with."
Valencia, who are looking to repeat their third-place finish last season, have also recalled Alves's former Almeria team-mate Sofiane Feghouli on loan and bought winger Pablo Piatti for 7.5 million euros from the relegated club, but the biggest signing could be 20-year-old attacking midfielder Sergio Canales, who is set to come on a two-year loan from Real Madrid.
Canales was one of Spain's brightest prospects at Racing Santander and many thought he should have stayed in Cantabria longer - a valid opinion as he started just 10 games under Jose Mourinho last season.
Canales wants to reignite his career, something Lionel Messi doesn't need to do, though Kempes would also like to see his compatriot reproduce his club form for Argentina.
"In a Barcelona shirt he shows he can be the best player in the world but we haven't always seen that for Argentina," he says.
The game in Washington? Barca lost 2-1 to a young Manchester United team. Barca can be beaten ... as long as they don't have Messi, Alves, Pique, Xavi and Puyol in the starting XI.
- Manchester United