The most goals in Thursday's play came in Bulgaria, where CSKA Sofia edged Derry City 3-2 to claim a narrow first leg advantage. Ioannis Pittas scored in either half for the hosts, who outshot Derry 17-6.
CSKA, who have participated in the Europa League proper on three separate occasions, qualified for the group phase in their most recent appearance six years ago, starting at this very stage.
It was looking as if The Candystripes would go into the decider down two goals, only for James Olayinka scored with two minutes to go to halve the deficit.
The League of Ireland side, based in Northern Ireland, are winless across three head-to-heads with CSKA, having been eliminated by them in the 2009/10 qualifiers.
Two-time UEFA Cup Winners Cup winners Dynamo Kyiv were held to a goalless draw versus Univseritatea Cluj in Lublin. Despite carrying the game - they had 27 shots, more than any other team on the day - the Ukrainian side could not find the back of the net.
Dynamo, who played in the Champions League or Europa League group phase every season from 2006 to 2023, have not reached the knockout stages since 2020/21.
Univseritatea Cluj, nicknamed 'The Students', conceded nine times to Levski Sofia in their two-legged UEFA Cup tie back in the 1972/93 season. That was their only other appearance in the tournament.
That was not the only game to end without a goal on Thursday, as Sheriff Tiraspol and Aluminij also ended 0-0. The Moldovan regulars had the majority of chances, but could not find their way past an Aluminij side making their European debut.
Experienced European sides prevail
The first player to score in this season's Europa League was Qarabag's Zakaria Sawo half an hour into his side's game versus Vestri. Abdellah Zoubir and Renaldo Cephas also found the back of the net for the home side in a comfortable 3-0 win.
Qarabag made the knockout round playoffs of the Champions League last term, but finished second in their domestic league. It was just the second time in the last 13 years in which they did not win the title.
Vestri, meanwhile, were playing their maiden continental match after they won the Icelandic Cup in 2025 despite suffering relegation to the second tier.
Ferencvaros, who reached the round of 16 in the UEL last spring, were also winners in their game, beating Vojvodina 2-1 away.
The Hungarian side scored with their only shots on target, with Nigerian forward Dele scoring the winner in the 88th minute. Like Qarabag, 'Fradi' regularly win their league, but saw their seven-year domination come to an end last ferm.
In Croatia, Hajduk Split scored once in each half en route to a 2-0 defeat of Slovak Cup winners Zilina. Roko Brajkovic put Hajduk ahead midway through the opening half before Dalisson de Almeida added a second four minutes after the break.
All six ties will be decided a week later, with the winning teams progressing to the second qualifying round to join 12 automatic entrants later this month.
The six defeated sides will transfer to the second round of UEFA Conference League qualification.
Follow all of the UEFA Europa League qualifiers on Flashscore.