Novak Djokovic suffered his heaviest ever defeat in a three-set match on Friday when he was knocked out of the Vienna ATP tournament by lucky loser Lorenzo Sonego, stalling his bid to wrap up the year-end world No 1ranking for a sixth time.
Italian Sonego, ranked 42 and who had initially lost in qualifying last weekend, is the first lucky loser ever to beat Djokovic.
His 6-2, 6-1 quarter-final stunner was 33-year-old Djokovic's heaviest ever defeat.
The only other time the Serb had won just three games was at the 2005 Australian Open at the hands of Marat Safin in a best-of-five set encounter.
"He just blew me off the court, that's all," Djokovic told atptour.com.
"He was better in every segment of the game. It was a pretty bad match from my side, but amazing from his side.
"He definitely deserved this result," added the Serb star who was playing his first tournament since his Roland Garros final defeat to Rafael Nadal three weeks ago.
Friday's defeat means Djokovic will have to wait a little longer before he completes the formality of equalling Pete Sampras's all-time record of ending the season top of the rankings for a sixth time.
"For sure it's the best victory of my life. Novak is the best in the world. Today I played so, so good," Sonego said.
"It's unbelievable. It's amazing. I played the best match in my life. I'm so happy for this."
Sonego fired 26 winners past the Serb who lost for only the second time in 2020. (He was also disqualified at the US Open).
Djokovic, a 17-time major champion, managed just seven winners against 25 unforced errors.
Sonego goes on to face either Britain's Dan Evans, who beat Grigor Dimitrov of Bulgaria 7-6 (7/3), 4-6, 6-3, for a place in the final.
Second seed and defending champion Dominic Thiem also lost on Friday, going down 7-6 (7/5), 6-2 to Russian world number eight Andrey Rublev.
Rublev hit 30 winners past the US Open champion and goes on to face South Africa's Kevin Anderson for a place in the final.
"I came here with the mood that I have nothing to lose," said Rublev who is chasing a fifth title of the year.
"I had already a really great season. I came here with zero expectations, just wanting to do my best. To try to fight every match. At the end, I am here in the semi-finals."
Anderson made the semi-finals by accounting for Russian fourth seed Daniil Medvedev 6-4, 7-6 (7/5).
It was 2018 champion Anderson's first top 10 win in two years.
Results from the ATP tournament in Vienna on Friday (x denotes seeding):
Lorenzo Sonego (ITA) bt Novak Djokovic (SRB x1) 6-2, 6-1
Dan Evans (GBR) bt Grigor Dimitrov (BUL) 7-6 (7/3), 4-6, 6-3
Kevin Anderson (RSA) bt Daniil Medvedev (RUS x4) 6-4, 7-6 (7/5)
Andrey Rublev (RUS x5) bt Dominic Thiem (AUT x2) 7-6 (7/5), 6-2