"It's a shame, we went for the win, and probably in our best period of the game they scored their second goal," Spain captain Busquets said.
"The group is a lot more complicated now and we don't have things in our own hands. We were going well, but perhaps lacked a bit of luck, but we have to continue - there's still a number of games to go, even if right now the scenario isn't the best."
Ferran Torres and Adama Traore were denied equalisers by fine Robin Olsen stops, while Robin Quaison should have sealed the win for the hosts in the third minute of stoppage time, only to lift the ball over the onrushing Unai Simon and wide after Eric Garcia's misplaced header.
Group leaders Sweden move onto nine points with three wins from three games, while Euro 2020 semifinalists Spain drop to second with seven points having played a game more.