David Ferrer proved much too strong for an out-of-sorts Novak Djokovic at the ATP World Tour Finals, thrashing the world number one 6-3 6-1.
Having enjoyed something of an escape against Tomas Berdych in his opening match at the season-ending tournament in London, Djokovic was simply blown away by the Spaniard in just 75 minutes.
Ferrer's stunning triumph, which follows on from a straight-sets win over Andy Murray, means he is now certain of a place in the semi-finals.
Djokovic, in contrast, must now beat compatriot Janko Tipsarevic in his final outing in Group A on Friday to make it through to the knockout stages.
"I think Novak maybe was a little bit tired today, he made a few mistakes," said Ferrer after handing the world number one just his fifth loss in 2011.
"But I played really well. I didn't make mistakes and for me this tournament is very important. Last year I didn't win a match and this year I've won two, so I'm really, really happy."
A shock was perhaps on the cards considering Ferrer's only victory over the Serb on an indoor court came in the same event four years ago.
Back then Ferrer went on to reach the final, and on his current form history could well repeat itself.
The fifth seed staved off a break point in the fourth game before forcing himself ahead in the seventh, a series of heavy forehands putting him 4-3 up.
A second break then gave him the set, Djokovic's 18th unforced error meaning he fell 1-0 behind for the second successive outing.
However, unlike against Berdych, the top seed was unable to battle back, raising concerns over both his form and fitness - he had arrived in the English capital having missed the Paris Masters due to a shoulder injury.
He was broken again at the start of the second set, defying two break-point chances on his own serve before Ferrer unleashed a powerful winner.
Another break gave the man from Valencia a comfortable cushion and he served out for the match, the end coming for Djokovic when he blazed a forehand well wide, summing up his poor performance.
"I have no words to explain it," Djokovic said afterwards. "It was the worst match I have played all year but all credit to David. He played really well."