Top American Mardy Fish booked his second ATP finals berth in as many tournaments, but this time he had to fight to hold off young compatriot Ryan Harrison. Harrison, 19, on Saturday kept his nerve in the face of a first-set onslaught and made world number nine Fish work hard to close out a 6-0, 4-6, 7-6 (7/3) semi-final victory at the $619,500 ATP hardcourt tournament in Los Angeles. In Sunday\'s final, Fish will face Latvia\'s Ernests Gulbis, who defeated doubles partner Alex Bogomolov of the United States 6-2, 7-6 (7/4). Gulbis will be playing in his second career ATP final. He won his only previous championship match, at Delray Beach in 2010. Gulbis had last reached a semi-final at Sydney in January. He reached a career-high ranking of 21 in February but a series of lackluster results has seen him drop to 84th. \"It\'s a very big win for me,\" said Gulbis, who fired 33 winners. \"I\'m on the way to a comeback. If I wouldn\'t win tonight I would drop to like, 1,000 (in the rankings).\" Fish who has surpassed Andy Roddick as the top-ranked American, has gone from strength to strength this season. He cruised past Harrison in straight sets in the semi-finals in Atlanta last week and went on to win the title. That was Harrison\'s first appearance in an ATP semi, and he showed on Saturday that he had learned a lot from the experience. \"He did most of everything better,\" Fish said. \"He was as tough a player to put away as I\'ve played.\" Fish, the top seed in Los Angeles, came out on fire, racing through the first set in just 20 minutes. \"That was as clean of a set as I could possibly play,\" Fish said of the opener. Although Harrison was clearly frustrated, he came out for the second set with renewed conviction. He held his serve with authority, and when Fish finally faltered, double faulting to give Harrison a break point and set point in the 10th game, Harrison pounced to seize the set. \"I didn\'t play a great game there,\" Fish said, who admitted he was feeling \"a little pressure\". \"You don\'t want to be in a third set,\" he said. However, he was full of praise for Harrison, who cracked the top 100 in the world rankings on Monday at number 94. \"He kept his level, credit to him,\" Fish said. \"He didn\'t let up. He could have easily won that match.\" Harrison said he just tried to keep his composure in the first set. \"There wasn\'t much that I did -- he played an awesome first set,\" Harrison said. \"For me it was a matter of getting on the board and making him feel a little pressure, hopefully.\" Although Fish gained an early edge with a break for a 2-1 lead in the third, Harrison broke back to knot the set at 3-3, held for 4-3 and pushed Fish relentlessly to the tiebreaker. In the tiebreaker, however, Fish\'s experience paid off as he quickly took a 5-0 lead and sealed the match on his first match point with his seventh ace. \"Tiebreakers are kind of a coin flip,\" Fish said. \"I was lucky to be able to apply some pressure early.\" Despite the defeat, Harrison said he had progressed since the previous weekend. \"This week the match against Mardy was a lot better,\" he said. \"It wasn\'t like I was overwhelmed by the situation. Today I really gave myself a chance.\"