Celtic showed they've narrowed gap, the board must now help Ange Postecoglou close it - Sean Martin

For a while - well, between the 56th and 82nd minutes - it seemed Celtic's long run without a competitive victory in Germany would finally be at an end.

Less than a quarter of an hour later it was actually the Hoops' nine-match unbeaten streak that had been left broken on the banks of the Rhine.

It was good while it lasted, though. Very good.

In many ways, it has been a season-sparking run. One defeat does not undermine the considerable progress and confidence that has been instilled any more than starring in The Ladykillers undermined Tom Hanks' 10-year stretch of movie magic.

Before the match, cautious optimism permeated the support and even manager Ange Postecoglou himself.

He spent a considerable portion of his pre-game presser hammering home the point that Celtic had played quite well when Leverkusen came to Glasgow, with an inability to keep their composure after conceding ultimately what allowed the game to get away from them.

Postecoglou's message centred around three things: focus; react positively to any mistakes; make an impact.

"It's not about eradicating individual errors, because they're human beings," he said. "They're going to make mistakes. It's how you immediately react to the mistake and what you do consequently.

"We’ll only learn from the game if we play our football. You’ll learn absolutely nothing if you go out there and shy away from it."

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So the question is did they measure up in those three key areas? Did they learn anything?

During the opening 10 minutes the Celts displayed decent composure in possession but with a distinct lack of penetration as Leverkusen, led down the right by Jeremie Frimpong, looked by far the more dangerous of the sides.

When they conceded in the 16th minute - thanks to Robert Andrich escaping Anthony Ralston to head home from a corner - it became all about that second message.

To their credit Celtic responded in exactly the manner Postecoglou wanted - which is to say, the opposite of the last time they played Leverkusen.

They settled their own nerves - and their manager's - by instantly resuming their attempts to control the ball and, gradually, that positive reaction turned the tide. They started to make an impact.

Josip Juranovic's Zidane-esque penalty shortly before half-time gave Celtic the initiative they saught before Joe Hart's bravery saved it and the combination of James Forrest, Kyogo and Jota kicked it up a notch.

But what about after going ahead? Same rules apply. Concentrate.

And they did. Leverkusen were held at arm's length for much of the next 20 minutes as Celtic got into something of a groove with the defence standing firm and Jota enjoying more freedom now that the game had opened up.

Then came the substitutions. On the 72nd minute Postecoglou withdrew Jota and Forrest for Mikey Johnston and Liel Abada.

The logic isn't hard to grasp - Forrest was never likely to complete 90 minutes on his first start since August while Jota had put in a shift. With Leverkusen likely to go for it and hints already that they were vulnerable to a swift counter - not least, the second Celtic goal - getting fresh legs out wide was an understandable move.

Kyogo exited a few minutes later, with Albian Ajeti on in his stead. The Japan international is crucial to the way Celtic play but his withdrawal was not unexpected; he has completed just three 90 minutes since joining the club, with one of those coming in the team's last game.

Jota celebrates putting Celtic 2-1 up against Leverkusen

Unfortunately, midfield anchorman Nir Bitton was forced off with a head knock at the same time as Kyogo was withdrawn. He was replaced by James McCarthy.

That unexpected loss of Bitton meant the whole front three and the deep-lying midfielder key to maintaining the groove Celtic had fashioned for themselves had been removed.

The Hoops plugged away for six more minutes before the dread hit. Andrich scored his second and this time an individual error - Ralston's panicked clearance after a heavy touch - was the trigger.

But, as Postecoglou said, mistakes happen. It's how you respond to them that matters. This time Celtic's reaction was not as convincing and, just a few minutes later, Leverkusen smashed in a third through Moussa Diaby with McCarthy's positioning suspect.

Going behind, strangely, proved to be more of a spark than the equaliser. The Hoops immediately tried to resume their gameplan and Turnbull went close at the end but, it must be said, Ajeti-Johnston-Abada is not quite the bedlam-inducing frontline of Kyogo-Jota-Forrest.

Therein lies the crux - and the difference. At this stage *insert weekly message about squad depth issues and the importance of January window in here* almost suffices without all the added details.

OK, fine. Whether it's acknowledging that quantity does not necessarily equal quality, that legitimate options on the bench are essential to the plan game-by-game or even simply that an element of belief must be shown in the manager, it's all different ways of saying the same thing. Celtic have a depth issue.

It's been the case since the summer transfer window shut. It was still the case during the September injury crisis. It was even the case during the nine-match unbeaten run.

Celtic may not have extended that to 10 in North-Rhine Westphalia but they certainly didn't depart Germany with nothing.

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They have their pride and, if they embrace it correctly, they will have the confidence that comes from knowing they took a side of a standard they will likely not face again this term to the very brink in their own back garden.

Postecoglou will surely make that clear to them in the days ahead - there were already traces of positivity in his full-time comments, even if the subtext was perhaps more to do with that pesky depth issue...

"There's still a gap between us and them and that's what we need to breach," he said post-match. "We gave ourselves a chance to pull off a great result but ultimately they're a good team and we just didn't finish the game off in the way we could've.

"Guys coming on didn’t have the impact we wanted - because we had some opportunities to create something ourselves and our decision-making wasn’t great. We allowed the pressure to build up.

"[But] credit to the players, Leverkusen are a fantastic team and we came here and gave them a game.

"They knocked us off 4-0 at home, we gave them a fright here. Hopefully next time that gap is even smaller.

"In all our European games we've taken it to our opponents so we'll bridge that gap if we keep taking this approach whenever we play these teams."

Absolutely.

Next up, in a quirk of fate, is Aberdeen - the team against whom the nine-match run started. They visit Parkhead on Sunday.

Going into that game Postecoglou will be telling his Celts the same three things as Thursday: concentrate; react positively; make an impact.

After all, one streak might have ended but that's no reason another one can't begin.