Qualifier Ryan Harrison battled from a set down to defeat sixth seed Ivo Karlovic and set up a Mexican Open semi-final against David Ferrer.
Fresh from dumping out reigning champion Grigor Dimitrov to reach the last eight, the American - ranked 169 in the world - continued his fine form this week with a spirited display that leaves him on the brink of a first career ATP singles final.
Harrison triumphed 4-6 7-6 (7-0) 7-6 (7-4) at the ATP 500 event before semi-final opponent Ferrer slogged it out until 02:16am local time (08:16am GMT) in his 6-4 3-6 6-1 victory over Bernard Tomic.
Karlovic will consider himself unlucky to be heading out of the competition after producing 16 winners and fended off all seven break points he faced.
However, the Croatian was unable to build on winning a tight first set that saw him take the solitary break in the third game.
Harrison saw three set points go begging in the second before dominating the tie-break and levelling at one set apiece at the fourth time of asking. He clinched the match in a decisive third-set tie-break.
Ferrer's love affair with the Mexican Open continued after the Spaniard won through against Tomic in a match that continued into the early hours.
The world number nine overcame a second-set blip to progress in a time of one hour and 41 minutes.
Ferrer will now go in search of a fourth title in Acapulco, having won the tournament in three consecutive years between 2010 and 2012, as well as finishing runner-up to compatriot Rafael Nadal in 2013.