Defending champion Steve Johnson beat Taylor Fritz at the US Men's Clay Court Championship to set up a final showdown against Tennys Sandgren.
American sixth seed Johnson squandered a chance to wrap up the match in the second set but left nothing to chance as he raced through the decider to secure a 7-5 6-7 (4-7) 6-2 win.
Johnson, riding high after ousting top seed John Isner in the quarter-finals, is chasing a third career ATP title when he faces Sandgren in the first career meeting.
Eighth-seeded Sandgren reached the first ATP singles final of his career with a 7-6 (7-2) 7-6 (7-4) win over 39-year-old Croatian Ivo Karlovic.
Sandgren, who had just two tour-level wins in his career prior to his run to the Australian Open quarter-finals in January, fell behind in the first set but recovered to seize control in the tiebreak, converting five of the last six points.
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The 26-year-old American then gave up a break in the second set when he double-faulted three times in one game but managed to recover again to set up another one-sided tiebreak.
Karlovic was looking to become the oldest ATP finalist since Australian Ken Rosewall won the 1977 Hong Kong title at the age of 43.
However, he leaves Houston with the distinction of being the oldest ATP semi-finalist since Jimmy Connors in 1993 by virtue of his quarter-final upset victory over Austrailian fourth seed Nick Kyrgios.
