* Davydenko loses two tiebreaks
* Monfils to face Tsonga in all-French semi-final (adds late matches, quotes)
Top seed Nikolay Davydenko slumped to a 3-6 7-6 7-6 defeat by Spain's Albert Montanes in the quarter-finals of the Open Sud de France on Friday.
Montanes will face Ivan Ljubicic for a place in the final after the Croatian fourth seed beat Finn Jarkko Nieminen 4-6 6-3 7-6.
The other semi-final will be an all-French meeting between second seed Jo-Wilfried Tsonga, who beat compatriot Gilles Simon 6-3 6-7 6-3, and Gael Monfils, a 3-6 6-4 6-4 winner against American John Isner.
Russian Davydenko hit 15 aces in a two-hour and 20-minute tussle in southern France but Montanes stood firm on his service games after dropping the opening set, winning the two tiebreaks 7-3 and 7-4.
Davydenko, the world number 11, is still hoping to snatch one of the three remaining spots for the season-ending Masters.
Tsonga, the world number 13, got off to the best start against Simon but a lapse in concentration in the second set tiebreak allowed his compatriot to level.
Tsonga, however, hit powerful forehands to break decisively in the sixth game of the decider.
His semi-final opponent, third seeded Monfils, resisted Isner's fightback to book his place in the next round.
"John is really tough to play. I surprised myself, staying calm throughout," Monfils told reporters.