Germany's Tommy Haas rallied to beat top seed and defending champion Andy Roddick 6-7 (1-7) 6-4 6-4 in the quarter-finals of the U.S. Clay Court championships.
The fifth seed needed two hours and 11 minutes to see off Roddick and advance to his fourth semi-final of the year.
It was a rare defeat on Houston clay for Roddick, who has claimed the title three times and came into the match with a record of 25-2 in the event.
Haas, who beat Roddick in the 2004 final, will next meet American wildcard Mardy Fish in today's semis.
Fish also needed to rally from a set down to dispose of compatriot Vince Spadea 4-6 7-6 (7-1) 6-2.
It will mark Fish's first semi-final appearance since 2004 in Halle where he lost to Germany's Rainer Schuettler.
Seventh seed Paul Goldstein reached his second semi-final of the year with a tidy 6-3 6-4 win over the Spain's Albert Montanes.
Goldstein will next meet Austria's Jurgen Melzer, who booked his semi-final place with a 7-5 6-4 win over Spain's Fernando Vicente.
"Today's match against a guy who grew up on clay for me is a great effort," said Goldstein. "It's one of my better wins.
"For a guy who's more comfortable on hard courts to beat a Spanish guy who loves the clay is a very satisfying win."
