Luka Stojkovic and Dion Beljo's first-half strikes ended Sunderland's unbeaten start to their Europa League campaign as Dinamo Zagreb earned a 2-0 victory on Thursday.
Sunderland's European form had been in stark contrast to their Premier League fortunes, but even with an improved second-half display, they were unable to mount a comeback.
Sunderland's intent for a fast start saw Dominik Kotarski called into action to push away Jules Ahoka's header, but the Black Cats found themselves behind in the 22nd minute.
Just moments after Granit Xhaka came to Sunderland's rescue to deflect Beljo's shot over the crossbar, the resulting corner from Mislav Orsic was cleared by the Sunderland captain but only as far as Stojkovic, who volleyed superbly past Robin Roefs.
Dinamo almost doubled their tally less than two minutes later when Orsic rounded Roefs, only to see his shot from inside the area cleared off the line by Thomas Meunier.
But Sunderland failed to heed that warning and conceded again six minutes before half-time. Josip Misic's long ball caught Meunier napping, with Stojkovic eventually feeding a clever pass into Beljo, who lofted into the back of the net.
Regis Le Bris responded by making a quadruple change at the break, and Sunderland thought they had reduced the deficit in the 47th minute when Wilson Isidor nodded in Xhaka's free-kick, only for the goal to be ruled out for offside by VAR.
The roar of the Stadium of Light crowd following that incident spurred Sunderland into life, and the hosts hit the woodwork twice in quick succession through Reinildo Mandava and Kevin Danso before Enzo Le Fee's volley was easily gathered.
Dinamo were happy to soak up the pressure in the minutes that remained, with Malick Fofana's tame effort in the 82nd minute the closest they came to altering the scoreline.
Dinamo end away day struggles to pile more pressure on Le Bris
Le Bris described Sunderland's campaign as a "new journey" with the Black Cats competing in the Premier League and Europa League, while also reaching the quarter-finals of the EFL Cup, but it remains to be seen how long the Frenchman will remain in charge at the Stadium of Light.
With the international break looming, Dinamo presented the perfect opposition to restore the feel-good factor at Sunderland ahead of facing Chelsea this Sunday, with the Croatian giants coming into the clash fresh from sacking Mario Kovacevic.
But Dinamo enjoyed a day to remember with Jerko Leko in temporary charge. They earned just their second win from their last nine away European matches (D4 L3), while they have now won four of their last seven European matches against English opposition (L3).
The damage came in the first half, with Dinamo registering an expected goals (xG) total of 1.17 from their eight shots to Sunderland's 0.43 from their five attempts, though the hosts did improve that to 1.6 by the full-time whistle, which was greeted with jeers by the home supporters.
Sunderland face Jagiellonia Bialystok in their next European game on November 26, but should the Black Cats fail to secure a positive result against Chelsea this weekend, the possibility of a new man overseeing that fixture could become a reality.