AMSTERDAM • Last season's Champions League semi-finalists Ajax came close to crashing out in qualifying on Tuesday before beating Paok 5-4 on aggregate.
On a night when former European champions Porto and Celtic were both knocked out, Ajax faced elimination when their former youth player Diego Biseswar scored in the 23rd minute to put the Greeks 3-2 ahead on aggregate.
Ajax captain Dusan Tadic saw one penalty saved but scored a second to draw level.
A Nicolas Tagliafico header put the Dutch team ahead in the 79th minute before Paok's physical style handed Ajax a third penalty which was converted by Tadic.
Biseswar scored again in stoppage time to again put Ajax in danger, but the Dutch champions held on to win 3-2.
Paok's players and staff surrounded the referee to protest after the final whistle of the third qualifying round match.
"It was a tough evening. I'm glad we got there in the end, but don't ask me how," Ajax midfielder Donny van de Beek said. "They're a very tough team to play against."
In the play-off round, the last stage of qualifying, Ajax face a likely easier task against Apoel of Cyprus, who beat Azerbaijan's Qarabag 3-2 on aggregate.
10 goals and seven assists in 20 European games for Dusan Tadic of Ajax Amsterdam.
The fact that Ajax even had to take part in qualifying prompted debate over Uefa's rules, which tend to favour less-storied teams from big countries over high achievers from smaller nations.
Their place in the qualifying rounds was due to the Dutch league's low ranking, despite their heroics last season.
By contrast, Italy's strong record means Atalanta get a group-stage spot despite never having played in Europe's top club competition.
Porto found their 1-0 first-leg lead wiped out as Russian side Krasnodar scored thrice in 34 minutes before running out 3-2 winners and 3-3 on aggregate to go through on the away-goals rule.
Krasnodar will face Olympiakos for a place in the group stage.
Romanian side Cluj scored two late goals to beat Celtic 4-3 on the night and 5-4 on aggregate after a tense game in Glasgow.
Red Star Belgrade, the 1991 European champions, came through 7-6 in a marathon penalty shoot-out after a 2-2 aggregate draw with FC Copenhagen. Both teams took 11 penalties apiece before Jonas Wind's miss sent the Serbian team through.
Wind and Red Star's Radovan Pankov took two penalties each because Red Star had finished the game with 10 men.
ASSOCIATED PRESS, AGENCE FRANCE-PRESSE