The summer signing from Hibernian headed home from an acute angle to bring Celtic level with just four minutes left in their first meeting with Gretna.

Scott McDonald's injury-time goal then took the champions back to the top of the Premier League with a 2-1 victory.

But Strachan felt his side could have avoided the late drama at Fir Park if they had opened up the game and provided more crosses for Killen.

The New Zealand international, whose first Celtic goal came on the eve of his 26th birthday, had not scored in eight substitute appearances.

But, after his flick-on following a long throw was headed back out by Gretna defender Chris Innes, he guided his header over Greg Fleming and just inside the far post.

"I felt sorry for Chris because I didn't think the lads round about him made it easy for him making his full debut," the Celtic manager said.

"I think he was hungry for it and if he got the right service he could score goals, but we weren't giving him the right service.

"I felt for Chris and I'm glad that he got that equalising goal, because he worked very, very hard and he deserved it.

"We were trying to thread balls through the middle on a bobbly pitch when we should have been switching the play more and getting more width to the game.

"But we persevered going through the middle and it wasn't good for them.

"What Chris needs is a bit more variation and he'll definitely create chances."

Gretna had taken the lead in the 37th minute when Fabian Yantorno curled a 30-yard free-kick around the wall and past the flat-footed Artur Boruc.

The Uruguayan could not believe Gretna had lost but took solace from their performance.

The First Division champions play St Mirren, Inverness and Falkirk in the coming weeks as they look to move off the bottom of the SPL.

"I think we had a great game," Yantorno said.

"Unfortunately the last five minutes were unbelievable.

"But I think we have to keep working hard and if we play like this we are going to win more games.

"We had a great game against probably the best team in the SPL.

"We have three important games coming up and we need to play like this."