Fifth seed Nikolay Davydenko beat Briton Andy Murray 7-5 6-4 to reach the semi-finals of the Dubai Championships on Thursday.
In another match, the sixth-seeded American Andy Roddick scored a straight sets win over the Spanish second seed Rafeal Nadal, winning 7-6 (5), 6-2.
The first set was an evenly contested affair but Roddick pocketed it in a tie-break and had little difficulty in the second. The win tied the American's head-to-head record with the Spaniard to 2-2.
Murray, who defeated world number one Roger Federer in the first round, began brightly and had chances to win the first five games but Davydenko fought off a break point in the second game and another at 2-1.
The Russian then earned a crucial break at 5-5 when Murray netted a double-handed backhand.
Murray held a break point to take the set to a tiebreak but Davydenko rose to the challenge with a backhand winner and took the set when Murray netted a return.
The Scot then had an opportunity to turn the match around, breaking to love as he built a 3-0 lead. But his advantage was short-lived as Davydenko broke back in the fifth game.
Although Murray had the chance to re-establish his lead with two break points at 3-2, Davydenko resisted and then broke for 4-3 by forcing a forehand error.
"I'm a bit disappointed purely because I had a lot of chances," Murray told reporters. "Early in the first set I had a couple of break points, and against someone like him, once he starts to get comfortable from the baseline, he's really tough to beat.
"You could do with getting a good start and I did that in the second set, but I played a bad game to lose my serve. I wasn't so disappointed the way I was hitting the ball. I was just disappointed I didn't take the chances that I had because I had quite a few."
Fourth seed David Ferrer was upset, losing 6-4, 6-3 to Feliciano Lopez in an all-Spanish match.
Ferrer, a finalist at the Masters Cup last season, broke to lead 2-1 before Lopez broke twice to take the first set.
Ferrer also broke to lead 1-0 in the second but again allowed his opponent back, dropping his serve for 1-1 and again to give Lopez a 3-1 lead.