ZAGREB, Croatia (AP) In a battle of big servers, Argentina's Juan Martin Del Potro beat Croatia's Ivo Karlovic 6-4, 6-7 (6), 6-3, 7-5 on Friday to leave the two teams tied at 1-1 following the opening singles matches in the Davis Cup final.
Del Potro, the 2009 U.S. Open champion who is capping a comeback after two injury-hit years, made the crucial break in the 11th game of the fourth set with a spectacular return of Karlovic's serve.
Del Potro broke the Croat in the opening game of the match and then held on to his serve to take the opening set. In the second, the Argentine appeared poised to clinch the tie-break after having a double set point, but Karlovic saved both and then sent the home crowd into frenzy as he forced two successive errors from Del Potro.
Del Potro cruised through the third set to get back into control.
''After losing the second set, I was a bit frightened,'' Del Potro said. ''Ivo was playing real well, but I managed to regain composure.''
Karlovic, who at 37 became the oldest man to play singles in a Davis Cup final in nearly a century, served 35 aces while Del Potro had 15.
''After winning the second set, I was hoping to continue like this, but my level went down a bit and his level went higher,'' said Karlovic who returned to the team after a four-year absence.
Doubles are played Saturday while reverse singles are scheduled Sunday, with team captains refusing to reveal which pairs they will use.
Croatian team captain Zeljko Krajan said he was satisfied with the result after the opening singles.
''Overall today I have to say I'm satisfied,'' Krajan said. ''It was hard to believe that we could have two wins today. We remain positive and optimistic.''
Argentina is the only nation in the Davis Cup's 116-year history to have reached four finals without winning the title. Croatia is targeting its second title after beating Slovakia in the final in 2005.
Croatia won the opening singles rubber after Marin Cilic struggled past Argentina's Federico Delbonis 6-3, 7-5, 3-6, 1-6, 6-2.
Cilic, the 2014 U.S. Open champion, looked like cruising to the expected easy victory until Delbonis broke the Croat twice in the third set, which ended on a Cilic double fault.
''I struggled on my return,'' said Cilic, the highest-ranked player in the final at 6th position. ''His (high) toss on his serve is a bit specific and it gave me problems.''
''I never said the match would be easy. After all, this is the final,'' Cilic said.
Delbonis started the fourth set 3-0 with a double break, and Cilic conceded the set on serve by netting an easy smash.
But after a bathroom beak, Cilic came back renewed and broke Delbonis to start the fifth set on the indoor hard court at Arena Zagreb. Cilic suddenly rediscovered his serving groove, and didn't give Delbonis a chance.
''I took a short break, talked to the coach,'' Cilic said. ''I was determined to start playing better.''
Cilic broke again in the seventh game, and served out after 3 1/2 hours, two hours longer than most expected.
Cilic served 17 aces in the match watched by some 12,000 fans, including thousands of Argentinians who outshouted the home supporters. Among them was former Argentine soccer star Diego Maradona.
''His serve was the key,'' Delbonis said. ''In the first two sets, he was serving unbelievably. When I started making some returns, things changed.''