Julien Benneteau and Nicolas Mahut delivered the doubles victory that sent reigning Davis Cup champions France back to the final, but Croatia were unable to claim the win they needed to advance against the United States.
Singles victories for Benoit Paire and Lucas Pouille on Friday put France on the brink and Benneteau and Mahut, both 36, did not drop a set in overcoming Feliciano Lopez and Marcel Granollers 6-0 6-4 7-6 (9-7).
Croatia also had a 2-0 lead after the first day of their semi-final with the United States but Mike Bryan and Ryan Harrison secured a 7-5 7-6 (8-6) 1-6 6-7 (5-7) 7-6 (7-5) success to keep alive the Americans' hopes of meeting the French.
That contest lasted four hours and 43 minutes in Zadar, where Croatia will still fancy their chances of winning the tie having won both of Friday's singles matches without dropping a set.
Veteran French duo Benneteau and Mahut had been paired against Granollers and Lopez in a match between four men with a combined age of 140 in Lille.
It was an astonishing start from the hosts as the Spaniards won just four points in an opening set that lasted only 18 minutes.
A miserable day continued for the Spanish pair as Lopez suffered a blow beneath his eye during the second set and though they led the third 4-1, the French would win the tie-break to seal an emphatic success.
Speaking after the match, Benneteau, who came out of retirement to play this doubles match, offered no assurances over his availability for the final later this year.
"It's quite possible it could be the last match of my career on tour," he said. "And what a way to finish."
The US, the tournament's most successful nation, could still meet the French in what would be their first final since 2007.
Bryan and Harrison were one set from victory but the Croatian pair of Ivan Dodig and Mate Pavic fought back to force a decider which the American duo won after a tie-break.
Bryan, who had come out of Davis Cup retirement at the age of 40 to play this game, said: "7-6 in the fifth, on the road and on dirt, this is right up there [with his best wins] and I will never forget this one."