Top seeds Nikolay Davydenko and Juan Monaco battled through two matches each on Thursday to reach the semi-finals of the Poertschach claycourt tournament.
World number four Davydenko and second seeded defending champion Monaco were forced to play second round matches in the morning and quarter-finals in the afternoon after heavy rain disrupted the start of the week at the Austrian event.
"I'm very happy but I'm also very tired," Monaco told reporters after following up a 6-2, 6-2 win over Czech Jiri Vanek with a 7-5, 7-6 victory over American Robby Ginepri.
"I don't remember the last time that I played two matches in one day but I hope to stay playing like this to reach the final."
Davydenko, seeking his third title at this event in four years, had an even tougher time of things, needing three sets to win each of his matches on Thursday.
The Russian recovered from a second set tiebreak loss to beat American John Isner 6-2, 6-7, 6-3.
He then came through another see-saw encounter to down Italian sixth seed Andreas Seppi 6-3, 1-6, 6-3.
Davydenko will now face fellow Russian and world number 96 Igor Kunitsyn for a place in Saturday's final.
Kunitsyn also came through two matches on Thursday, beating Slovenia's Blaz Kavcic 6-1, 6-4 before seeing off the last remaining local favourite Juergen Melzer, dampening the Austrian's 27th birthday with a 6-4, 3-6, 6-3 defeat.
Monaco will take on Croatian third seed Ivan Ljubicic who made tough work of his only match on Thursday, defending six match points against Spain's Daniel Gimeno before winning their quarter-final 6-3, 4-6, 7-6.
"It was very tough and I did think it was all over," said Ljubicic, who is now within sight of his first ever ATP claycourt final.
"But the main thing is that I won and it would be great now to reach the final."