"I thought we had the game under control for three quarters, we defended well and we could run and score easy baskets. But then we broke down, lost our game and they took the momentum into overtime," said Gasol, whose brother Pau is sitting out the event.
Spain had a similar meltdown against Slovenia and is clearly missing the likes of Pau Gasol, Serge Ibaka and Juan Carlos Navarro.
In the first quarterfinal Wednesday, Spain will play Serbia. Serbia has the youngest team in the tournament and has been inconsistent, also losing three games, before a sound victory over 2011 finalist France.
Serbia lost the 2009 final to Spain, was fourth at the 2010 world championship, but then flopped at the Europeans two years ago and failed to qualify for the last year's London Olympics.
The Serbs have nine newcomers, including as guard Nemanja Nedovic who outplayed Tony Parker in the win over France. Nenad Krstic has been one of the better centers in the tournament.
"They move the ball well, they play hard defense, they are strong at both ends of the court," Spain coach Juan Orenga said of the Serbs.
In the second quarterfinal Wednesday, Slovenia plays France. On Thursday, Croatia plays Ukraine and Lithuania goes against Italy.
Italy has the smallest team in the tournament and could struggle against Lithuania's big men Jonas Valanciunas and Donatas Motiejunas. Lithuania was bronze medalist at the 2010 worlds but has not made the podium in Europe since the 2007 bronze and lost in the quarterfinals at home two years ago.
Since winning the silver medal at the 2004 Olympics, Italy has not been able to reach the quarterfinals in any major competition, and failed to qualify for the last two Olympics and one world championship. It missed the 2009 Europeans as well and finished 17th two years ago.
"This was a good win for my players who had a great desire to play such a game - in the last few years we could see Spain only on TV," Italy coach Simone Pianigiani said.
"It was the first time I was playing against Spain at senior level and I think we all wanted to see if we can compete," Datome said.
"We beat probably the best team in the tournament," Italy guard Pietro Aradori said.
France has been inconsistent as well despite the presence of Parker and other NBA stalwarts such as Boris Diaw, Nicolas Batum, Mickael Galabale, Johan Petro and Nando de Colo.
The French have lost three games as well but their size could prove too much for Slovenia, which has a shorter bench and may rely too much on the shooting of Goran Dragic.
Croatia is trying to make the podium at a major tournament for the first time in 18 years. It has sharp-shooting guards in Bojan Bogdanovic and Krunoslav Simon and a good big man in Ante Tomic.
Ukraine has been the biggest surprise, along with the early elimination of Russia and Turkey and the failure of Greece to make it into the last eight.
The Ukrainians won three tight games to advance under their American coach Mike Fratello. They have some size and a good shooter in Sergii Gladyr.
Ukraine, which will host the tournament in 2015, is in the quarterfinals for the first time.
"We are beginning to benefit from years of hard, systematic work," said Sasha Volkov, a former forward for the Soviet Union and now the president of the Ukrainian basketball federation.
"In two years' time I expect that we'll do even better. We are missing some players here but we have good young players and I think a good future," Volkov said.
"We are young and ambitious," Gladyr said.