Walcott settles Arsenal's nerves and clinches a place in last 16

Arsenal 3 Partizan Belgrade 1

Infuriatingly complacent one minute, cruising into the Champions League knockout round the next, it needed Theo Walcott to remind his Arsenal team-mates last night that there is no such thing as a free passage through this competition.

If ever there was a performance that showcased the different faces of Arsène Wenger's team then it was this one. Having toyed with one of the weakest teams in the Champions League, Arsenal conceded an equaliser and had to confront the uncomfortable possibility they might go out of the competition until Walcott put them back in control.

And along the way, Arsenal lost Bacary Sagna to a red card that means he will miss the first leg of the next round. Top of the Premier League, in the Carling Cup semi-finals and now into the first Champions League knockout round, but Arsenal still like to make things difficult for themselves.

Wenger takes a great deal of pride in his record of qualifying for the knockout stages of the Champions League every year for the last 11 including this one, and it would have been an ignominious way to lose the record last night. By the time Samir Nasri scored the third it was comfortable – although that had not always been the case.

There is a familiar attitude among Wenger's richly talented players that, once they are ahead, the result will take care of itself. Last night it cost them an equaliser scored by forward Cleo, who struck after Arsenal had failed to extend their lead beyond Robin van Persie's first-half penalty.

At that time, had Braga scored against Shakhtar Donetsk, Arsenal would have been heading out and although the Ukrainians eventually won that game 2-0, there was some anxiety at the Emirates. Having lost their last two group games to Donetsk and Braga, it was not inconceivable Arsenal would make a mess of this one too.

Donetsk's win meant Arsenal finished second in Group H, as expected, so they will face one from Barcelona, Real Madrid, Schalke or Bayern Munich in the draw for the next round on 17 December. Van Persie said boldly that "as a football fan" he would prefer Barcelona or Madrid.

The pragmatists would say Arsenal should settle for Schalke before they set their sights on the big names. They also lost Kieran Gibbs to yet another ankle injury last night – "unbelievable," said Wenger – and he will have a scan this morning. He left the Emirates on crutches and will not be available for Monday's game at Manchester United.

Wenger said that if the choice was given to him between playing the next round in Spain or Germany, "I don't know [which one I would prefer]." He added: "For you journalists, you might prefer to go to Spain. For us, not necessarily. Let's be realistic, Barcelona are super-favourites in this competition at the moment. But we will take what we get and if it is Barcelona then it is Barcelona. We have played them already this year and we will see."

Seven months on, Wenger can still frame a plausible argument that his team should have done better against Barcelona in the Champions League last season. Having drawn 2-2 at home, they went 1-0 up at the Nou Camp and lost 4-1 but even the most devout optimist would struggle to see Arsenal beating Barcelona at the moment.

It is in defence that the problems lie for Arsenal. It was the same again last night when Celo was allowed room to shoot on 53 minutes and his effort took a generous deflection off Sébastien Squillaci on its way into the goal.

Monday's game against United will give Arsenal some idea of their readiness for the challenges that the next round in February could bring.

Partizan are a poor side who played above themselves last night although not when Marko Jovanovic tripped Van Persie as he was going away from the target. The goal from the spot was Van Persie's first since the last game of last season against Fulham.

Walcott came on after Cleo's goal and there was a murmur of approval when the disappointing Andrei Arshavin was summoned as the man to make way for him. With 17 minutes left, Walcott seized on a poor clearance by Jovanovic and restored the lead.

Finally Arsenal had found their stride. Substitute Nicklas Bendtner and Sagna combined well on 77 minutes to craft an opening for Nasri. He thought about passing it but decided to clip it into the corner for Arsenal's third.

"It was harsh," was Wenger's judgement on Sagna's red card for pulling down Aleksandar Lazevski when he was the last defender. It was certainly daft. But Arsenal are through and they have until February to get it right for the next round.

Arsenal (4-2-3-1): Fabianski; Sagna, Squillaci, Koscielny, Gibbs (Eboué, 22); Denilson, Song; Nasri, Van Persie, Arshavin (Walcott, 67); Chamakh (Bendtner, 75). Substitutes not used: Szczesny (gk), Rosicky, Vela, Wilshere.

Partizan Belgrade (4-4-1-1): Stojkovic; Savic, Jovanovic, Krstajic, Lazevski; Babovic (Davidov, 80), Medo, Petrovic, S Ilic; Moreira (Brasanac 90); Cleo. Substitutes not used: R Ilic (gk), Stankovic, Kizito, Iliev, Smiljanic.

Referee: P Tagliavento (Italy)

Booked: Partizan: Krstajic.

Sent off: Arsenal Sagna (86)

Man of the match: Nasri.

Attendance: 58,845

Group H

Results: Arsenal 6-0 Braga, Shakhtar 1-0 Partizan; Partizan 1-3 Arsenal, Braga 0-3 Shakhtar; Braga 2-0 Partizan, Arsenal 5-1 Shakhtar; Partizan 0-1 Braga, Shakhtar 2-1 Arsenal; Braga 2-0 Arsenal, Partizan 0-3 Shakhtar; Arsenal 3-1 Partizan, Shakhtar 2-0 Braga.

Shakhtar Donetsk 2-0 Braga

Two goals by Razvan Rat and Luiz Adriano in the last 12 minutes secured top place for the Ukrainian side and ended Braga's slim hopes of progressing.

Last 16 Qualifiers

Group A Tottenham, Internazionale

Group B Schalke, Lyons

Group C Manchester United, Valencia

Group D Barcelona, Copenhagen

Group E Bayern Munich, Roma

Group F Chelsea, Marseilles

Group G Real Madrid, Milan

Group H Shakhtar Donetsk, Arsenal

Draw takes place in Nyon on 17 December. Group winners face runners-up, teams from same country cannot be drawn together.