Olivier Giroud felt his heart race as time appeared to slow. In the words of Arsenal's £13m striker, "the dream start" beckoned. Eighteen minutes into his debut for the club as a substitute, he found himself clean through, thanks to Santi Cazorla's clever pass. He simply needed to steer his right-foot shot into the corner.

If he scores, Arsenal win, he is the hero and the healing process over Robin van Persie's departure to Manchester United begins. Instead, Giroud's shot kept on travelling past the post. Arsène Wenger, the manager, threw up his hands and slumped into his seat. Everybody in the stadium suspected that Van Persie would have found the net. "It just didn't smile for us today," Giroud said.

Wenger always takes defeat badly, and this result felt like a defeat, despite the worthiness of Sunderland's defensive effort and the pair of decent early chances that they created for James McClean and Jack Colback.

Yet it was startling to see how weary Wenger looked afterwards, as was the sense of resignation in his words and body language. He confirmed that Alex Song was bound for Barcelona in a £15m deal which, as things stand, means he has turned a profit on his summer transfer spend.

With Van Persie and Song absent and Lukas Podolski, Cazorla and Giroud wearing the red shirt for the first time, there was a sense that another cycle has started. After overseeing so many of them, Wenger could have been forgiven for feeling the grind.

It felt appropriate to ask him whether he still had the enthusiasm for it all. "I believe that part of our club is to influence people's lives in a positive way," he replied. "You would prefer to influence it in a positive way for yourself but it does not always happen."

Van Persie's departure has hit him hard and Martin O'Neill, the Sunderland manager, said that the situation was "as bad as it gets". Song's case is more curious. The midfielder's desire to explore his options led to friction with the club while his consideration of his worth to the team, in technical and financial terms, differed to that of Wenger.

Arsenal had Song under contract to 2015 but their readiness to accept Barcelona's offer spoke volumes. It is easy to detect a feeling at the club of good riddance. Wenger is expected to push ahead with his move for Real Madrid's Nuri Sahin, although he said that he has sufficient existing options to cope.

Song, though, is the latest in a line of players to have developed impressively at Arsenal, only to leave. "We make the players here," Wenger said. "All that have left were made here or made a name here or came here very young. Fábregas, Clichy, Adebayor, Henry, Nasri, all of them. Song came at 17. He had a lot to do when he arrived but he did it."

Wenger's challenge is to get the best out of his new signings. He said that he sees Podolski as his centre-forward, which raises the question of whether Giroud, a true No9, can expect to start regularly. Podolski, who was disappointing on Saturday, did play as the centre-forward for Cologne last season, but he has tended to play off the left for Germany.

"That's where I see him [as the centre-forward]," Wenger said. "But he has some work to do to change his game … to make runs in behind, protect the ball and move around the box. When you come from a wide position, it's not easy straight away to find all that."

It was put to Wenger that Arsenal might have to play differently with Podolski as opposed to Van Persie. "Maybe," he said. "I have to study the game and see what he did when we had the ball. At the moment, we cannot say it worked."

O'Neill could be relieved at Giroud's miss but delighted at Sunderland's collective resilience. His thoughts, though, were also coloured by transfer-market business. He is desperate for reinforcements, particularly up front. "What we lack is some quality in major positions and I actually think the quantity, too."

Man of the match Lee Cattermole (Sunderland)