Borna Coric and Marin Cilic led Croatia to a 2-0 win against hosts Spain in the Davis Cup to set up a last-four clash against Australia.
Coric fought hard to beat Robert Bautista Agut 6-4 7-6 (7-4) in the first contest on Wednesday in Malaga.
In a match that lasted just shy of two hours, Coric hit 12 aces on his way to tying Mario Ancic for fourth place in Croatia's all-time leaders in the Davis Cup with his 13th singles win.
"I didn't know that fact to be honest," the 26-year-old said on court. "It's a very nice fact, Mario is a legend of Croatian tennis and obviously it does mean a lot to me that I am there with him."
His experienced team-mate Cilic had a harder time of things, needing to come back from a set down to overcome Pablo Carreno Busta 5-7 6-4 7-6 (7-5) in a thriller.
Like Coric, Cilic relied heavily on aces, smashing 20 through the contest, but he was made to sweat by Carreno Busta, who took the first set.
Cilic fought back to win the second, and was a break ahead in the third before his Spanish opponent broke back and looked set to take the tie to a rubber clash in the doubles.
The decider went to a tie-break though, with Cilic coming back from 4-1 down to seal victory for his country in front of a disappointed Spanish crowd.
Croatia will now face Australia on Friday after they defeated the Netherlands 2-0 on Tuesday thanks to wins for Jordan Thompson and Alex De Minaur.