Spain have won both their games in group D without conceding a goal and Turkey have lost both of theirs without scoring.
Croatia's match against the Czech Republic was held up for several minutes after their fans threw flares on to the pitch and began fighting among themselves.
Eight flares and other objects landed on the pitch near to riot police, who had been deployed in front of the section housing Croatia fans.
The trouble broke out in the dying minutes of a game that Croatia were leading 2-1.
Croatia, sanctioned three times during the qualifying competition, are already facing a disciplinary hearing on after fans threw flares and ran on to the pitch during their opening match at the finals against Turkey in Paris.
The English referee called the players to the centre of the pitch and consulted an official after the trouble broke out, while Croatia's players appealed for calm from the fans.
Play eventually resumed with the Czechs scoring an equaliser with a penalty to salvage a 2-all draw.
In the day's other match Italy also advanced to the last 16 with a 1-nil win over Sweden.