ARSENAL boss Arsene Wenger last night praised Alexis Sanchez after he helped his team reach the Champions League's last 16.

The Chilean striker netted the crucial second goal that sealed a 2-0 win over Borussia Dortmund at the Emirates Stadium.

The Gunners had gone ahead after only a minute when Yaya Sanogo netted his first senior goal for the club.

But it was Sanchez who made the game safe in the 57th minute with a great curling shot. And his manager was unstinting in his praise of the forward, who has won rave reviews since his summer arrival from Barcelona.

Asked what he brought to the team, Wenger said: "Unbelievable fighting spirit and class as well.

"Alexis is a mixture of talent and desire."

One sour note for Wenger was the loss of Sanogo and Mikel Arteta to injuries, with the former Rangers midfielder of particular concern.

"We think Mikel has a calf injury. It doesn't look good," Wenger said. "It's difficult to take on the chin at moment. We have so many games and need everyone available."

Arsenal had thrown away a 3-0 lead at home to Anderlecht a fortnight ago and lost to Manchester United on Saturday.

This time round their defending was faultless.

Wenger said: "We had the focus to defend well together. It was a similar game to Saturday but we focused really well not to give any chances away."

And centre-half Per Mertesacker added: "It was good to go in front so quickly, but we had to play another 89 minutes.

"We played absolutely solid and that was key. It was a solid performance defensively. We didn't give them much, especially in the second half."

The German World Cup winner added: "We have had a few disappointing results so this was a mental test. But we are strong enough and now we can continue.

"After Anderlecht and after Manchester United we dropped mentally a bit, but we learned from those disappointments and we are delighted with the performance here."

Arsenal's next match is away to West Bromwich Albion in the Premier League on Saturday.

Mertesacker said: "We have to prove ourselves because last season we dropped a lot of points.

"Now we have to focus on the Premier League."