Wayne Rooney reached the 100-goal milestone for Manchester United on Saturday and Michael Owen opened his account for the Premier League champions who roared back to form with a 5-0 thrashing of Wigan Athletic.
United, surprisingly beaten 1-0 at promoted Burnley in midweek, were toothless before the break but Rooney's header early in the second half opened the floodgates for the visitors.
Abou Diaby led free-scoring Arsenal to the top of the table, scoring twice in a 4-1 home defeat of Portsmouth to follow up last week's 6-1 rout of Everton.
Manchester City joined Arsenal and United on six points with a 1-0 home victory over promoted Wolverhampton Wanderers while Sunderland also earned their second win of the season, coming from a goal down to beat Blackburn Rovers 2-1 with Kenwyne Jones twice on target.
Hull City defeated Bolton Wanderers 1-0, their first win in the Premier League since March 4, and Birmingham City's 0-0 stalemate with Stoke City was the first draw of the season.
It took a while for United to turn their superiority into goals at Wigan, who gave a debut to French midfielder Mohamed Diame.
Former Wigan winger Antonio Valencia, the man tasked with filling the gap left by Cristiano Ronaldo's transfer to Real Madrid, unlocked his old club's defence after 56 minutes.
With time and space to cross, he picked out England striker Rooney who made no mistake with a header to notch a century of goals for the club he joined from Everton in 2004.
United keeper Ben Foster made a fine save to deny Hugo Rodallega a minute later and in a frantic spell the visitors, going for a fourth consecutive title, doubled their lead through Dimitar Berbatov.
Rooney's second, a deflected shot, killed off Wigan before Owen struck with a shot that went in off the post. Nani made it 5-0 in stoppage time with a Ronaldo-like free kick.
Arsenal maintained their storming start to the season, which included a 2-0 Champions League playoff first leg win at Celtic in the week.
However, they enjoyed a large slice of luck that left Portsmouth manager Paul Hart fuming.
Trailing 2-1, Portsmouth had a good chance to level three minutes after the break when Nigerian John Utaka outpaced William Gallas and was through on goal before being brought down by the French defender.
Gallas escaped punishment and bottom club Portsmouth did not even win a free kick. Minutes later the Arsenal player made it 3-1.
"It was an amazing decision, a clear-cut penalty and red card," Hart told reporters. "Then Gallas scores. It shows you what a cruel game it can be. I'm mystified."
Diaby opened the scoring on 18 minutes following clever play from Eduardo down the left and the midfielder added his second after being played in by Emmanuel Eboue.
Portsmouth pulled a goal back before halftime through Younes Kaboul. After Gallas's escape and tap-in, substitute Aaron Ramsey capped a satisfying afternoon for the Gunners with a well-taken fourth.
"We always feel we can score goals from anywhere," said manager Arsene Wenger. "We have scored 10 and we could have scored more, it's a brilliant start."