In a matchup of past Delray Beach champions, German second seed Haas squandered three break points in the 11th game of the third set.
Gulbis won the last five points to hold for a 6-5 lead, then won six of the last seven points in the tiebreaker.
France’s Roger-Vasselin upset US top seed John Isner 6-4, 4-6, 6-4 in the other semi-final.
Gulbis, ranked 109th in the world, is seeking his third ATP title at the same event where he won his first tour crown in 2010.
Former world No. 2 Haas was denied a chance at a 14th career title at the same event where he won the 2006 crown.
Roger-Vasselin finished with four aces and three double faults, winning 63 percent of his second-serve points against the American.
BRAZIL TENNIS CUP
AP, FLORIANOPOLIS, Brazil
Monica Niculescu of Romania defeated Olga Puchkova of Russia 6-2, 4-6, 6-4 in the final of the Brazil Tennis Cup to win her first WTA title on Saturday.
The 75th-ranked Romanian broke Puchkova’s serve to go up 5-4 in the final set, then converted on her service game to close out the match in 1 hour, 59 minutes.
“It’s unbelievable,” Niculescu said. “This means a lot, I was so nervous and wanted to win this so much. My game was not brilliant today, but it shows that in tennis if you keep fighting you can manage to win.”