Borna Coric beat Roberto Bautista Agut 6-4, 7-6(4) to give Croatia a 1-0 lead over hosts Spain in their quarter-final tie at the Davis Cup Finals in Malaga on Wednesday.
Coric was solid from the service line as he fired down 12 aces and turned aside the only break point he faced en route to securing the victory in just under two hours.
Coric broke to go 4-3 up in the opening set and after Bautista Agut held to love in the next game it was the Croatian who saved a break point to hold serve and close out the frame.
The two players then combined for five love holds during a tightly-contested second set during which neither faced a break point before Coric raced out to a 4-1 lead in the tiebreak and then secured the win on his third match point.
Marin Cilic can now secure Croatia's place in Friday's semi-final against Australia with a victory over Pablo Carreno Busta in the day's second singles match.
However, defeat for Cilic wold mean the teams will play a deciding doubles rubber where Nikola Mektic and Mate Pavic would face Spanish pair Carreno Busta and Marcel Granollers.