Davydenko's strong serving helped him beat Federer
World number one Roger Federer crashed out of the Qatar Open in Doha at the semi-final stage as he again came unstuck against Nikolay Davydenko.
The Russian, who also beat Federer in their last meeting in the semis at November's ATP World Tour Finals in London, triumphed 6-4 6-4.
Davydenko will play Rafael Nadal in the final after the Spaniard earlier made short work of Viktor Troicki.
The world number two dominated the Serbian to claim a 6-1 6-3 victory.
Federer faced 10 break points against Davydenko as his serve let him down badly - he managed to get only 55% of first serves in, compared to the Russian third seed's 79%.
The Swiss saved seven of those break opportunities, including five in the first set, but managed just a solitary break of serve himself.
Davydenko, who has won four times out of five on hard courts against Nadal, is full of confidence after his second successive win over Federer.
"Before I lost 12 times in a row to Federer, but because I beat him in London I felt like I really could win," Davydenko said.
"I still had the level I had in London, and that was good - but I don't know how long I can keep it up."
Federer, who has had six matches in eight days, did not seem too concerned about the setback.
"I have to get my unforced errors down, but apart from that I moved well and I didn't think my performance was too bad," he said.
"Nikolay played well when he needed to play well. He got ahead and got the momentum and that helped him. Then he played the big points well and deserved to win."
Nadal converted three of his four break points in a one-sided opening set, winning an impressive 65% of points on Troicki's first serve.
The Spaniard set up four more break opportunities in the second set, taking two, as the Serbian again struggled to cope with the four-time French Open winner's powerful returns.
Troicki also claimed a late break of his own, but it merely delayed the inevitable.