The Scotland midfielder had been on the end of criticism from a section of the Parkhead support for failing to find the net since arriving from Hearts in January in a $3million deal.

Hartley, 30, was left out of this season's opening two Clydesdale Bank Scottish Premier League games but replaced Aiden McGeady against Spartak Moscow in the Luzhniki stadium where be bulleted home a 21st-minute opener.

Three minutes from the interval, Spartak striker Roman Pavlyuchenko headed the equaliser but Celtic are firmly in the driving seat for the return game in a fortnight's time.

Hartley told PA Sport: "It was a nice time to score my first goal for the club and it is a bit of a weight lifted off my shoulders.

"I've had a bit of criticism since I came to the club but that's part and parcel of playing for Celtic.

"It was a great ball from Scott McDonald and I just attacked it.

"But I think I had forgotten how to celebrate!

"There will be times during the season when you are not going to play but I'm not the type of player who will 'chap' the manager's door.

"I'm happy that there is a big squad and there will be rotation during the season.

"It will be tough game in two week's time but we have managed to get that all-important goal."

Manager Gordon Strachan hailed his side as heroes after their positive result against the leaders of the Russian Premier League.

And the Celtic boss explained why he drafted in Hartley for McGeady.

He said: "I'm very proud of them. It was a good performance and an exciting game.

"We had a very young side out there and there were a few players making their debut.

"I'm very pleased with the way they handled the situation. Spartak had nine wins out of their last 12 games and they are top of the league.

"It was a good time for Paul to score his first goal for the club and it is valuable.

"I thought we needed people who were defensively very good.

"Aiden is doing very well but he plays further up the pitch and dribbling may have been a problem for him because of the surface.

"I was happy with the way it worked out."

Strachan reaffirmed his pre-match criticism of the artificial pitch and looked forward to playing on grass at Celtic Park in the return game.

He said: "What made it harder was the surface played completely different from how it was when we trained on it.

"Spartak played well but they have had plenty of practise on that pitch.

"The atmosphere will be good and I'm looking forward to playing there.

"I'm sure we will be more at home on our surface."

Spartak Moscow coach Stanislav Cherchesov was defiant despite Celtic being favourites to go through to the group stages.

He said: "The tie will be decided at Celtic Park. I am disappointed but nothing is over yet."