Davis Cup Final, Croatia v Argentina: Marin Cilic & Juan Martin del Potro win on day one

Del Potro beat Andy Murray during Argentina's semi-final win over Britain

Juan Martin del Potro beat Ivo Karlovic in four sets to bring Argentina level with Croatia in the Davis Cup final at the Zagreb Arena.

Del Potro came through 6-4 6-7 (6-8) 6-3 7-5 to leave the best-of-five tie locked at 1-1 after day one.

"I was nervous after I lost the second set, in the end I had to take the longer road to victory," he said.

Marin Cilic had earlier given Croatia the lead with a thrilling 6-3 7-5 3-6 1-6 6-2 win over Federico Delbonis.

Del Potro added: "The atmosphere was fantastic. Our fans were great but the Croatian fans were brilliant too and showed us a lot of respect. It was an exhausting match but I think I will be OK for the rest of the weekend."

Croatia's Ivan Dodig and Frank Skugor will take on Argentina's Leonardo Mayer and Guido Pella in Saturday's doubles.

The home side won their first and to date only Davis Cup title in 2005, while Argentina, who beat reigning champions Great Britain in the semi-finals, hope to finally win the title after losing in four previous finals.

Cilic, the highest-ranked player in the tie at sixth in the world, let a two-set lead slip before prevailing against Delbonis in three hours and 30 minutes.

"The crowd helped me to stay in there, it was not easy," said Cilic.

"Federico played great tennis from the middle of the third set to the end of the fourth. Just at the beginning of the fifth, I tried mentally to stay in there and get that break, and it was a huge difference."

Argentina football legend Diego Maradona was among those watching in the Zagreb Arena