Laurent Koscielny praised the strength in depth in the Arsenal ranks after Olivier Giroud marked his first Premier League start of the season with a Boxing Day late winner against West Bromwich Albion.

Having played second fiddle to Alexis Sanchez for much of the campaign, injuries to Theo Walcott and Alex Oxlade-Chamberlain gave Giroud a chance in Arsene Wenger's starting line-up.

On what was looking like a frustrating afternoon as the Gunners struggled to break down the West Brom rearguard, who had goalkeeper Ben Foster in particularly fine form, Giroud headed home an 87th-minute effort to earn a 1-0 victory.

French defender Laurent Koscielny has praised the strength in depth in the Arsenal ranks

West Bromwich Albion forward Salomon Rondon challenges Koscielny (left) on Boxing Day

The win keeps Arsenal within sight of London rivals Chelsea, who are nine points clear of Wenger's men at the league summit, and defender Koscielny believes Giroud's temperament while being on the sidelines has been exemplary.

'He stayed focused with the team,' France international Koscielny told Arsenal's official website.

'We are not 11 or 18 players, we are 25 players. All the players who play for Arsenal have a big part to play during the season because of injuries and suspensions, and everyone needs to be ready to fight for this club.

'Olivier started and he tried to give his best on the pitch. He fought and it's good for him to score the winning goal.

'It was so important because last week we lost two games in seven days and we wanted to get back to winning three points.

'It was a hard game because West Brom play with their qualities, which include making big blocks, and that made it hard for us to find a good solution.'

Arsenal went into the clash having lost their previous two outings at Everton and Manchester City, results which saw them slip further away from in-form Chelsea, and Koscielny admitted the players needed the morale boost of returning to winning ways.

'We lost the first game of the season (against Liverpool) and we came back with a good run and a lot of wins,' he added.

Olivier Giroud netted in the 87th minute to ensure Arsenal clinched a vital three points

'We lost two games in a week last week and it was very important to come back with a win. The confidence will come back when you win and the most important thing now is to continue to win games in a row so that hopefully we can get into the first position.'

The Baggies have now lost three of their last four games, albeit to Chelsea, Manchester United and Arsenal.

Foster was in superb form as he kept out efforts from Sanchez, Iwobi and Giroud before being beaten by the forward's header.

And the England-capped goalkeeper conceded it was a bitter pill to swallow, especially after such a strong team performance.

'It's tough to take,' Foster told West Brom's official website.

Victory for Arsenal means they stay nine points behind Premier League leaders Chelsea

'They were the better team and had a lot more chances and possession than us. Saying that, to lose any game in the last three or four minutes is always hard to take.

'Giroud is a good, strong player and it was a good header so fair play to him. The result reads 1-0 and we have to take it and get on with it.

'You get to the last five minutes of any game and you'd like to think that you could shut it out. When you come to a place like the Emirates and it's still 0-0 after 85 minutes you'd be really happy.