Top seed Nikolay Davydenko has been knocked out of the ATP Pilot Pen tournament, the Russian losing 6-3 3-6 6-4 to American Sam Querrey in Connecticut.
The hard-serving Querrey fired 15 aces in all but found himself down 15-40 in the pivotal ninth game of the third set.
However, he won the next four points, two on aces, to go 5-4 uo before breaking Davydenko to love to close out the match.
"I just took a couple of deep breaths and just really focused on my first serve and fortunately hit two big first serves in there," the sixth seed said.
"You see that a lot when you save break points, that next game a lot of times you see guys go ahead and convert the break, that's kind of what happened."
Querrey opened the match with two aces and won eight consecutive points on his way to a 3-0 opening-set lead.
His serve reached speeds of 135 mph but he also mixed things up, going wide at times and also hitting serves into Davydenko's body.
"I have no chance because (of his) first serve," said Davydenko, who cited his opponent's power as the reason why he called a doctor to look at his right wrist midway through the match.
Querrey will face Argentina's Jose Acasuso in the last four after he beat fellow unseeded player Florent Serra 7-5 6-4.
Russian Igor Andreev also advanced into the semi-finals, the seventh seed beating Argentina's Leonardo Mayer 6-4 6-7 6-3 to set-up a last four showdown with second seed Fernando Verdasco, a 6-3 6-1 victor over Jurgen Melzer.