Ireland's London 2012 gold medallist Katie Taylor suffered a surprise defeat in her semi-final at the Olympic qualifying tournament in Turkey.
Azerbaijan's Yana Alekseevna handed Taylor her first defeat in five years to leave the five-time world champion still seeking Olympic qualification.
Lightweight Taylor will still qualify for Rio if she reaches the semi-finals at the World Championships in June.
Alekseevna, 28, won a unanimous verdict although it looked a close fight.
Taylor, 29, was last beaten at a multi-nations tournament in Bulgaria in 2011.
Taylor handed first defeat in 63 bouts
But she followed that with a run of 62 straight victories which included her Olympic final triumph four years ago.
In addition to her Olympic success and five consecutive world titles, Wicklow woman Taylor has also won six European titles, five European Union gold medals plus a European Games triumph last summer.
Alekseevna, beaten in both her previous two contests against Taylor, was able to pick off the Irishwoman in the opening round in Samsun as she was given a 10-9 verdict on all three cards.
Taylor's more counter-punching strategy did bear some dividends in round two as two of the judges scored her a 10-9 winner.
However, Alekseevna was in firm control after a cagey third round as she took a 10-9 verdict on all three cards.
Taylor looked to have done the better work in the final round but the Azeri fighter was given the verdict by two judges to complete a 39-37 win on all three cards.
The Irishwoman held her right hand aloft as the result was about to be delivered and appeared stunned afterwards.
Taylor congratulates victor Alekseevna
Taylor later said that the contest had been "very close and could have gone either way".
"It's always been such a close contest between us," added the Olympic champion.
"The difference between winning and losing is marginal. Today wasn't my day. Congratulations to her. She deserved it."
Taylor insisted that she would regroup for the defence of her world title in Kazakhstan, where a semi-finals spot will be enough to secure Rio qualification.
"I've had losses before and come back from them and I'll come back again.
"Thank god, I've got another chance to qualify (for the Olympics) at the World Championships."