's-Hertogenbosch - Ivo Karlovic outserved his fellow Croatian Marin Cilic on Saturday to book a spot in his first ATP Tour final of the year against Gilles Muller at the grasscourt event in 's-Hertogenbosch.
The 38-year-old, whose best surface has always been grass due to his 2.11m frame, edged out former US Open champion Cilic 7-6 (7/4), 5-7, 7-6 (7/2) after two-and-three-quarter hours.
Luxembourg's Gilles Muller, 34, stands between Karlovic and a ninth career title, after he sprung a surprise by beating second seed Alexander Zverev 7-6 (7/5), 6-2 in the first semi-final.
Sunday's final will have the oldest combined age for two players since Ken Rosewall (42) and Ile Nastase (30) went head-to-head in Hong Kong in 1976.
The battle of two of the game's biggest servers saw Karlovic save a set point in the 10th game, before going on to take the opener in a tie-break.
But top seed Cilic, who has reached the Wimbledon quarter-finals for each of the last three years, hit back to force a decider thanks to the only break of the match at the end of the second set.
Karlovic, helped by 29 aces in the match, shored up his serve though and, despite missing a match point in the 12th game, cruised through another breaker to move into his 18th ATP final.
The left-handed Muller went into his match with Germany's rising star Zverev as a definite underdog, but edged in front in a first-set tie-break.
The world No 10 Zverev fell apart in the second to hand Muller a straightforward victory, as the top two seeds both bowed out of the tournament.
On the women's side of the draw, Estonian Anett Kontaveit beat Lesia Tsurenko to reach her second WTA Tour final, where she will play Russia's Natalia Vikhlyantseva.
The 21-year-old Kontaveit, at a career-high ranking of 49th, overcame a second-set blip to see off her Ukrainian opponent 6-3, 6-7 (0/7), 6-2.
Vikhlyantseva, 20, claimed an impressive 6-3, 7-5 victory in the other last-four clash over fifth seed Ana Konjuh to reach her maiden top-level final, as she continues a fantastic season that has seen her break into the world's top 100 and make her first Grand Slam appearances.
Results from the ATP and WTA tournaments in 's-Hertogenbosch on Saturday (x denotes seeding):
Gilles Muller (LUX x4) bt Alexander Zverev (GER x2) 7-6 (7/5), 6-2
Ivo Karlovic (CRO x3) bt Marin Cilic (CRO x1) 7-6 (7/4), 5-7, 7-6 (7/2)
Natalia Vikhlyantseva (RUS) bt Ana Konjuh (CRO x5) 6-3, 7-5
Anett Kontaveit (EST) bt Lesia Tsurenko (UKR x7) 6-3, 6-7 (0/7), 6-2