Delray Beach - South Africa's Kevin Anderson toppled top-seed John Isner 7-5, 7-6 (7/4) on Saturday to reach the ATP final at Delray Beach, where he will face Australian qualifier Marinko Matosevic.
Matosevic, ranked 173rd in the world and appearing in his first career ATP tour semi-final, beat Israel's Dudi Sela 5-7, 6-4, 7-6 (9/7).
He faces a tricky task to overhaul the seventh-seeded Anderson, after the towering South African came out on top in a battle of big servers.
Both Anderson and Isner fired 16 aces, but 11th-ranked Isner also had three double faults - including one on the first point of the second-set tie-breaker which gave Anderson the opening he needed.
Anderson quickly jumped to a 3-0 lead in the 'breaker, and while Isner fired two aces to narrow the gap to 5-4, Anderson promptly won his next two service points to seal the victory.
The South African's crisp return game saw him break Isner once in the first set, but he saved the only break point he faced in the match in the second game of the second frame.
"Really excited," Anderson said. "I couldn't have played a better match today. I knew I had to really take care of my service games, and I served really well, especially in the tie-breaker."
Although Matosevic was a somewhat unexpected finalist, the 36th-ranked Anderson said he would not take him lightly.
"I'll have to play well," Anderson said. "Marinko's come all the way through qualifying, so he's obviously playing well."
Matosevic, 26, became the first qualifier to reach the final at Delray Beach since Evgeny Korolev, who was runner-up to Mardy Fish in 2009.
Matosevic seized a 5-2 lead in the final set, but failed to convert two match points as he served for the match at 5-3. Sela broke, then held to knot the set and spur the tie-breaker.
Matosevic again seized the advantage, taking a 3-0 lead, but wasted two more match points before finally closing it out after two hours and 54 minutes.
The last qualifier to win an ATP title was Finland's Jarkko Nieminen in Sydney in January.