Read Matt Dickinson's match report

Arsène Wenger admitted to feeling physically sick after the shock of the 2-1 defeat against Hull City on Saturday, but, at the Emirates Stadium last night, the Frenchman received the perfect pick-me-up. Showing no ill- effects from the Barclays Premier League debacle, his Arsenal side cruised past Porto 4-0 to kick-start their Champions League group G campaign.

It was Arsenal at their best after a few initial hiccups and the ease with which they brushed aside the Portuguese champions augurs well for their hopes of reaching the knockout stages. Victory took Arsenal to the top of their group and stretched their unbeaten home run in the competition, encompassing Highbury and the Emirates, to 23 matches.

Wenger had given most of his players the chance for atonement — he left out only Emmanuel Eboué from the starting line-up against Hull, bringing in Samir Nasri — and they responded in style. Perhaps stung by further criticism in the match programme, in which Wenger accused them of displaying a “careless attitude”, they banished any lingering blues from the biggest upset in the top flight this season.

“I was tempted to make more than one change, but I didn’t want to give the feeling that I punish one more than the others,” the Arsenal manager said. “Sometimes you give a team the chance to respond quickly. I made one change because Nasri is a more natural left-sided player.

“On Saturday I believe that we were caught. Maybe at 1-0 up we thought the job was done. It is down to your memory how quickly you can forget and it is part of the learning process. This team is maturing and it was the response I wanted.”

Arsenal had been unconvincing in their opening group match, against Dynamo Kiev in Ukraine a fortnight ago, needing a late equaliser to force a 1-1 draw. They started off little better against Porto, who went close to taking the lead three times in the early stages through Cristián Rodríguez and, twice, Lisandro.

Rodríguez’s header had struck the bar and, at that stage, Wenger may have felt the nausea of Saturday returning. “That was the real time we were lucky,” he said. His team did not look in rude health, either, but they recovered their senses and never looked back. Robin van Persie and Emmanuel Adebayor both scored a goal in each half, Adebayor’s second a penalty. “Yes, I expect to win the group from here,” Wenger said. Van Persie was more guarded. “It’s only the second game of the competition,” the striker said. “If you want to win it, you have to win so many games.”

Manchester United also rediscovered their form after an opening draw against Villarreal in group E, Dimitar Berbatov scoring twice — his first goals for the club — in a 3-0 win against Aalborg in Denmark. “I knew they would come sooner or later,” Berbatov said. “I helped the team to win — that’s the important thing.”

However, United’s joy was tempered by injuries to Paul Scholes and Wayne Rooney. Scholes will be out for at least six weeks, according to Sir Alex Ferguson, the United manager, after suffering medial ligament damage to his right knee, while Rooney, who scored their first goal, limped off with an ankle problem. He will have a scan today.

Celtic’s hopes of a first group-stage win away from home in 16 attempts were dashed when they lost 1-0 against Villarreal.