Isco has called on Spain to stop their "hesitant" approach to matches and sharpen up their play in the knockout phase of the World Cup.
La Roja snatched a 2-2 draw with Morocco on Monday to secure top spot in Group B and book a showdown with host nation Russia in the last 16.
Spain's performance was far from convincing, however, with Iago Aspas scoring an equaliser in second-half injury time after a VAR referral saw the referee overturn an initial offside call.
Fernando Hierro's side had fallen behind to a Khalid Boutaib strike 14 minutes in and Morocco looked set to claim the victory in Kaliningrad when Youssef En-Nesyri headed in nine minutes from time, after Isco had equalised in the first half.
Aspas spared Spain's blushes and secured their place at the top of the group, but Isco says they should be concerned about the way they are starting games in particular.
"Again, we've gone onto the pitch a little bit hesitant," he told Telecinco. "It can't keep happening to us. From now on, the games start as life or death. We can't keep gifting goals, we have to focus.
"We're lacking what we know how to do best, which is to control the game and to have the ball.
"Every team from now on can send us home. Even Morocco, who didn't have anything to play for... nobody is going to give you anything. You have to play easier, not commit mistakes with the ball, not let them score with a lost piece of possession...
"We don't have to go crazy, although it's true we're first, but we have to do things better.
"We know it will be very difficult from now on, with the hosts, who are having a fantastic tournament. We have to do things very well."
Morocco players were furious to see Aspas' goal given after VAR's intervention, although replays seemed to show the Celta Vigo forward was just onside.
Isco, however, says the technology is to everybody's benefit.
"That's what it's for, so they don't take the point away from us that we won," he added. "It favours everyone."