Estonia 0-1 Spain Isco's strike, five minutes before half-time, gave Spain a slender win in Tallinn and put them in a commanding position in Group 5.
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Isco was the matchwinner as Spain edged past Estonia to put the reigning champions in with an excellent chance of reaching the play-offs.
Despite scoring six without reply against these opponents on matchday two, Luis Milla's side again dominated but found the going tougher in Tallinn as they struggled to break down a resilient defence - with a fine performance from Estonian goalkeeper Marko Meerits at their heart.
The custodian showed his quality after 17 minutes, tipping away a Marc Muniesa header, although he could do nothing about Spain's goal five minutes from the break. Muniesa charged down the right flank and from the byline picked out an unmarked Isco, who fired in with ease.
Estonia – and notably Igor Subbotin – tried to attack in the second period but were again grateful to Meerits, who first confidently saved Rodrigo's header and later showed excellent alertness to race out and prevent Tello from scoring.
Spain could not find a way past Meerits for a second time but their job had been done. Should second-placed Switzerland fail to win in Croatia on 2 June, the Roja's play-off place as section winners will be guaranteed.