Top seed Li Na crashed out of the Qatar Total Open on Thursday after going down to a surprise defeat to Czech qualifier Petra Cetkovska.
Li, who will move to a career-high second in the world rankings next week following her Australian Open triumph, lost 6-7 (2/7) 6-2 4-6 in a third-round match lasting two hours and 46 minutes.
Both players committed five double faults and lost their serve twice in a nervy first set which 29-year-old former world No 25 Cetkovska eventually won on the tie-break.
But Li hit back to level the match courtesy of two breaks of serve in the second set.
She would have been expected to go and claim victory in the decider but lost her serve three more times playing some tentative tennis as Cetkovska, ranked 134th in the world, claimed a famous win.
"She played well. I don't think I was playing so bad," Li said. "Maybe, sometimes the wrong choice made me lose a lot of important points."
There were no such worries for the other five top seeds in action on Thursday.
Cetkowska will face sixth seed Angelique Kerber, who crushed Klara Zakopalova 6-2 6-3, while fifth seed Jelena Jankovic, who saw off wild card Alisa Kleybanova 6-1 6-2 in 72 minutes, will now play third seed Petra Kvitova - the Czech requiring a third set to see off compatriot Lucie Safarova 7-6 5-7 6-2.
Fourth seed Sara Errani battled from a set down to beat Romania's Monica Niculescu 2-6 7-5 6-1, while second seed Agnieszka Radwanska eased past Mirjana Lucic-Baroni 6-4 0-1, the Croatian retiring early in the second set.