Top seed Nikolay Davydenko tumbled out of the St Petersburg Open in the second round, going down to Croatian qualifier Marin Cilic 1-6, 7-5, 6-1 on Thursday.
The Russian was cruising to a comfortable win after taking the first set in 27 minutes, but the 102nd-ranked Cilic broke the world number four late in the second to level the score before racing through the decider to record a memorable victory.
Earlier, defending champion Mario Ancic was sent packing by Russian third seed Mikhail Youzhny 6-4, 6-2.
Youzhny, the 2004 champion, earned one break in the first set and two more in the second to secure a quarter-final dual with seventh-seeded German Philipp Kohlschreiber.
Ancic, who is returning to the top level after being forced to miss most of the year with mononucleosis and a shoulder injury, had reached the quarter-final at last week's Madrid Masters but said he was feeling unwell before the match.
"I don't want to take anything away from his victory as he played a really good match, but I was not feeling very good since the warm-up," said the world number 37.
FEELING DIZZY
"I was feeling dizzy and weak because of what happened to me this year, which is normal. I knew that this could happen to me any day. I still have some ups and downs and today I was not feeling very good," the Croat added.
"But he played very well, taking the ball early and serving very well. He deserved to win.
"I'm happy with my comeback so far. I played well in the three tournaments and I just want to work hard to keep getting better and get my energy back. I know this is a transition period for me after not playing for so long."
Youzhny said he simply outplayed his opponent.
"I served and returned well today. I didn't have any problems on my serve until the last game while he had trouble on his serve since the opening game of the first set," the Russian told reporters.
Looking ahead to his match with Kohlschreiber, who beat Youzhny in the second round of this year's US Open and leads their head-to-head meetings 3-0, the Muscovite said: "I'm not aiming for revenge, I'll just try to win tomorrow.
"The fact that I haven't beaten him doesn't mean much. I was 0-6 against [Ivan] Ljubicic before finally winning one," added Youzhny, referring to his victory over the big-serving Croat in the Rotterdam final earlier this year.
Britain's second seed Andy Murray faces Czech qualifier Lukas Dlouhy in the last match on centre court.
