A late penalty from Robert Pires secured a 1-0 win over ten-man FC Thun in Switzerland on Tuesday night. But the Gunners boss is acutely aware that much tougher tests lie ahead than that offered by the Swiss minnows.

"This will give us confidence but we are not going to go overboard," Wenger said.

"It was important to finish the job and top the group. It means we have the second game at home in the last 16 and will play against the second team of another group.

"But that does not necessarily mean we get the easiest draw. It is a different competition now. With direct knockout, the real competition starts."

Arsenal made hard work of breaking down Thun after their defender Armand Deumi was dismissed in the 34th minute for pulling down Robin van Persie after the Dutch winger had sprung their offside trap.

"It was a good quality game as long as it was 11 against 11," reflected Wenger.

"The referee had no choice but once their player was sent off the level of the game dropped.

"We lost our concentration a bit and they had less resources to put us under pressure, although they were still dangerous on the break."

Arsenal would have had an easier result but for an off-night from captain Thierry Henry, who marked a club-record 70th European appearance by missing a number of chances.

"We didn't really play well, we should have played more of our passing game," Arsenal defender Philippe Senderos admitted after his return to his native Switzerland.

"Thun took hold of the match, they gave us trouble. But the important thing is we came away with the three points."

Thun remain in third place in the group with three points and will secure a slot in the UEFA Cup with a draw in their final group match against Sparta Prague in the Czech Republic.