Mikel Merino hit a brace for Spain after coming on as a substitute for the world champions
Mikel Merino hit a brace for Spain after coming on as a substitute for the world champions © MARKO PERKOV / AFP
Ivan Perisic put hosts Croatia ahead but substitute Merino equalised for Spain early in the second half.
Perisic was sent off with 10 minutes remaining for a second yellow card and Merino helped Spain capitalise with a fine finish to reach the last eight with two matches to spare.
"I'm very happy to be able to help the team, another game in which it was my turn to score from the bench," Merino told TVE.
"I'll go out there with the best possible attitude even while frustrated about not being able to play more... but this team is a family and that always shows."
Spain went a 42nd consecutive game without suffering defeat and lead England by three points at the top of Group A3.
Slaven Bilic's Croatia were crushed 7-0 by England on Saturday, in front of a crowd of children as home fans were banned for racism, and came out determined to make it up to their supporters in Split.
Spain goalkeeper Unai Simon was called into action early on, saving well from Josip Stanisic's header, as Luka Modric's team impressed in the first half.
A few minutes later the hosts took the lead in Split with Simon saving from Igor Matanovic's shot but Perisic reacted quickest to head home the rebound.
Athletic Bilbao goalkeeper Simon put Aymeric Laporte in a tough spot in his own box with a loose pass and Croatia intercepted and almost grabbed a second. However Simon saved from Freiburg striker Matanovic's effort.
Spain's teenage star Lamine Yamal raced through on goal early in the second half but he fell after nudging the ball past Barca team-mate and Croatia goalkeeper Dominik Livakovic.
Merino, on at the interval, pulled Spain level in the 61st minute with a low finish after Dani Olmo, who developed in Croatia as a youngster, fed him.
Croatia's task of holding on in the final stages became harder when Perisic brought down Marc Cucurella and was dismissed.
Merino, so often making key impacts from the bench for Luis De la Fuente, including in the World Cup this summer, finished the job with his second of the night.
The former Real Sociedad man, with two minutes remaining, produced a superb turn and finish to blast past Livakovic.
"We look upwards, but with our feet on the ground," said Merino of Spain's ceiling.
"(We go) with humility -- there are days like today when the (unbeaten) streak can become complicated."