The result means the South London side are now in the draw for the round of 16 on Friday, where they will meet either AEK Larnaca, who they faced earlier in the group stages, or Mainz.
Palace boss Oliver Glasner made three changes to his squad with Guessand, Lacroix – who came off injured in Mostar a week ago – and Daichi Kamada coming into the XI while Chadi Riad, Will Hughes and Yeremy Pino moved to the bench.
In the first leg last Thursday, some Palace fans were chanting that Eagles’ boss Oliver Glasner was getting ‘sacked in the morning’ after the South London side had drawn 1-1. A few hours after returning to London, Glasner had his response, urging fans to ‘stay humble’.
Whether the words were meant in the manner they were received was up for debate, but a toxic atmosphere had affected the relationship between the most successful manager in Crystal Palace history and a section of the fan base.
Guessand’s last-minute winner against Wolves last Sunday had eased the situation, providing a second win in 16 games and despite many empty seats inside Selhurst Park on Thursday, the home fans got behind the team from the very first minute. m
Against Zrinjski, Palace started positively in attack and their first chance came after six minutes, with record signing Jorgen Strand Larsen finding space only to see his shot deflected off by Duje Dujmovic for a corner.
The chances were flowing with Kamada seeing his 23rd minute shot deflected behind for a corner, and then Ismaila Sarr’s shot deflected out six minutes later.
With 35 minutes gone, Zrinjski were breaking up the game with fouls and injury breaks, frustrating the home fans, something which Zrinjski coach Igor Stimac said was part of his game plan. He knew his side could not outplay Palace.
And just as the game could have become one of attrition, a moment of quality from Adam Wharton saw his free-kick land on the head of Lacroix in the six-yard box, with the unmarked French defender heading home with ease. It was the eighth time in 10 European games this season that Palace had gone ahead first.
Zrinjski sliced through Palace four minutes later, with Leo Mikic only able to shoot wild and high in front of the Holmesdale Road – a sign of how vulnerable Palace can be in transition.
The second half saw more attacking from the home side, with Sarr nearly through just two minutes in, but Zrinjski got in behind again soon after to unsettle the home fans.
After Wharton got an early yellow card in the second period, Glasner hooked him to avoid the referee making the decision for him, bringing on Hughes.
But it did not unsettle the home side as a pair of Kamada free-kicks caused problems in the Zrinjski defence.
Zrinjski did have a goal disallowed two minutes later when Matej Sakota was miles offside after receiving the ball for Karlo Abramovic to slot home.
As Glasner looked to close out the game, former record signing Brennan Johnson came on for Stand Larsen with just over 15 minutes remaining – he was lively in-behind.
The attacking threat continued with Guessand forcing a great save from Goran Karacic, and Sarr heading wide before seeing his shot in miles of space saved by the Bosnian goalkeeper with five minutes remaining.
There was nervousness in SE25 as the clock counted down, but Guessand ensured no one needed to worry as his second consecutive late goal in the space of five days ensured history continues for the Eagles.
The result made it two consecutive wins for Palace for the first time since last December, when they recorded Premier League wins over Burnley, Fulham and then a UEFA Conference League victory over Shelbourne last December – all away – and arguably the peak of Palace under Glasner.
What a difference a week makes.
Lacroix: In Glasner we trust
Maxence Lacroix praised under-fire manager Oliver Glasner after navigating a difficult spell at Crystal Palace.
Reaching the last 16 of the Conference League came as a relief for Glasner, with the manager enduring a tough seven days since their 1-1 draw away in Mostar last week, with supporter protests and intense speculation over his immediate future.
However, back-to-back home wins have brought some of the feel-good factor back with Lacroix backing the manager and his winning mentality.
“He's a big gaffer. He's a good coach and he proved it by winning two trophies in two years. He has the ability to give us everything to win,” said Lacroix after the game.
“We have shown it before, and now we are back on it. We have worked hard for that. We are happy that we won and can continue the journey. We scored early, a fast goal and it made us happy. When we have good deliveries, it's easier to score – we have trained for it.
“It was a perfect night for us,” he added to TNT Sport. “We were a little bit angry in our last result against them but, in our house, we showed that we have the quality in this tournament and we are really happy to win in front of our fans. It’s beautiful, we are really happy because we deserve it and the journey continues.”
That journey could end with the Conference League final in Leipzig in May, but next up is the last 16, with Palace to learn their opponents at 13:00 on Friday.
“We have to go game-by-game. This competition is not easy. We can see every time it is difficult to go and play away or even to play in our house, but today we made the job so this is the most important for us,” he said.
“We have to be respectful and if we play our football, there is a big chance to achieve good results. Every single competition [whether it’s] the Premier League or the UEFA Conference League, we will give 100% because this is our job, and this is why we are.”