With an hour gone at Parkhead on Thursday, hope in the stands was in short supply.

Celtic were 1-0 down against Besiktas and heading towards a fourth straight defeat in this season's Europa League.

Manager Martin O'Neill turned to his bench for a spark, bringing on Callum Osmand and Camilo Duran to replace Sebastian Tounekti and James Forrest out wide.

The impact was almost instantaneous.

Osmand's first touch nestled in the bottom corner of Alexander Nubel's goal, just 43 seconds after the 20-year-old attacker came on.

All of a sudden, Celtic had a threat in behind and Besiktas looked rattled.

Then, on 77 minutes, O'Neill withdrew Kasper Hogh after another underwhelming display from the club record signing and moved Duran through the middle.

Again it had the desired effect.

Osmand played Duran through with a delightful pass and the Colombian rounded Nubel before slotting Celtic into the lead.

Orkun Kokcu levelled for Besiktas with a fine strike, but Duran had the final say two minutes later, controlling Kieran Tierney's scuffed shot and beating Nubel from close range to send the home support into ecstasy.

"Everything changed with the subs; Osmand coming on and Duran going through the middle," former Celtic midfielder Stiliyan Petrov said on TNT Sports. "They freed up space for Nygren and Baur. It was a really positive 30 minutes."

Not since Johannes Edvaldsson against Jeunesse d'Esch in the European Cup in September 1977 had a Celtic substitute scored twice in Europe (excluding qualifiers).

"Osmand came on, first touch put the ball in the net and that's really difficult, he can definitely score a goal. Duran has been fabulous for us all season no matter where he plays," O'Neill said of his goalscorers.

The Northern Irishman was asked whether it was a case of inspired substitutions or rather evidence that he should have started his best players.

"I'm not standing up for myself, not at all," he said.

"It was in design to do exactly what it did. We've played nine games in 25 days, some players needed a breather and you can get re-energised from coming on the field.

"I'm going to say that that was our plan and those players were going to come on the pitch at some point in the game."

Numbers point to Duran as solution

The contrast between Celtic's attacking play with Hogh leading the line and with Duran through the middle was stark.

The £11m Dane's effort cannot be questioned. He continued to battle to try to make things happen, but since arriving from Bodo/Glimt in the summer, he has now failed to score in 16 of his 17 Celtic appearances.

In 77 minutes against Besiktas, he didn't have a single shot and managed just one touch in the opposition box.

Duran, meanwhile, played just half an hour and scored two goals, had two shots, and registered four touches in the Besiktas box.

O'Neill has previously said he is unsure of his best team, but it is now obvious that Duran is Celtic's best option through the middle.

Despite Hogh's price tag, it feels inevitable he will be among the Celtic substitutes for high-stakes games.

"It'll be tough for Hogh," Hearts defender Craig Halkett said on TNT Sports. "He was the big-money singing but it's not coming off for him.

"As a player you need to keep your head down, keep working hard and hope it turns."

Osmand too appears to have pushed himself to the front of the queue to start off the left. The former Fulham man is direct and evidently has an eye for goal, with a happy knack for scoring in big games.

"This is a great team we're playing against," Osmand told TNT Sports. "Camilo [Duran] did amazing, he's such a poacher. Credit to him.

"It's a lot harder starting games. The team dug in, stayed strong and we got our rewards.

"[The goal] caught me off guard, but I'm just glad I caught it nice. I just want to come on and make something happen. So happy with tonight."