Arsenal's lack of passion and the burgeoning Rooney - van Persie partnership feature in our analysis of Manchester United's 2-1 victory.
Robin van Persie showed just what Arsenal are missing as the defeat by Manchester United illustrated his old side are not serious title contenders this season.
All eyes were on Van Persie in his first meeting against his former employers and the Dutchman did not disappoint with a goal and starring role at Old Trafford.
After 10 games of the season, Arsenal find themselves nine points behind leaders United and their subdued performance will not give much hope to Gunners fans of a concerted push for the title.
Here, Pete O'Rourke reflects on the action.
Manchester United boss Sir Alex Ferguson stuck to the starting XI that helped them beat Chelsea last weekend with Van Persie leading the line, ably supported by Wayne Rooney.
Tom Cleverley and Michael Carrick anchored the midfield with Ashley Young and Antonio Valencia providing the pace down the wings.
Arsenal boss Arsene Wenger also kept the same side that narrowly overcame Queens Park Rangers in the Premier League last week.
Theo Walcott found himself on the bench despite his goalscoring heroics in the midweek Capital One Cup win over Reading.
For United, it was the traditional 4-4-2 formation with Rooney playing slightly deeper to help the midfield playing behind Van Persie.
Valencia impressed against Chelsea last weekend and the winger was again instructed to provide the width for United down the right with Young on the left.
Arsenal chief Arsene Wenger employed a 4-5-1 formation as he packed the midfield and played Lukas Podolski to provide support for Andre Santos down the left.
Aaron Ramsey was used out wide on the right with Olivier Giroud ploughing a lone furrow in attack which only changed when Walcott was introduced in the second half.
Ferguson showed all his experience and knowledge by bringing off Cleverley just past the hour mark with the midfielder teetering on the brink of a red card.
Cleverley was lucky to escape a red card as, when already on a booking, he hacked down Jack Wilshere, but he got away with only a ticking off by referee Mike Dean.
Ferguson admitted after the game he took off Cleverley for Anderson to save the England international from being sent off with the Brazilian adding some impetus to United's midfield for the closing stages.
Wenger finally answered the calls of the travelling fans when he brought on Walcott early in the second half for the ineffective Ramsey.
At 2-0 Walcott was moved up to a central attacking role, but he had little impact for Arsenal.
Andrey Arshavin came on for the final eight minutes for the subdued Podolski, but the Russian had little time to make an impression.
Mike Dean had a busy game handing out seven yellow cards, including a red card for Jack Wilshere.
The official got it right to send off Wilshere for two bookable offences, but he made a mistake in not sending off United's Cleverley before that for a foul ironically on Wilshere.
Dean, though, did get the award of the penalty to United right when he adjudged Cazorla to have handled Wayne Rooney's cross inside the box.
Van Persie was the best attacker on the pitch and he could have scored more than the one goal he netted against his old club.
The Dutchman gave the Arsenal defence a tough time and showed his killer instinct with a finish with his right-foot for the opening goal.
Patrice Evra also popped up with a rare goal and was solid at the back as United prevented Arsenal from creating too many clear goalscoring opportunities.
Vito Mannone prevented Arsenal from losing by a bigger margin with a number of impressive saves.
The keeper, who started as third-choice before the season kicked off, showed he is an able deputy for the Gunners in the absence of the injured Wojciech Szczesny with another commanding display.
Mannone had no chance with both goals, but worryingly for Arsenal he found himself a little too busy at Old Trafford with a number of his team-mates failing to shine.
United will be happy that they didn't need to play well, but still came away with all three points.
Sir Alex Ferguson admitted after the game his side were not at their best, but they still ground out the result.
Worryingly for their rivals, United are now top of the table despite not hitting top form so far this season.
Another warning for the rest of Premier League is the burgeoning partnership between Van Persie and Rooney.
The pair are beginning to gel together and if these two start to fire, it will be hard for the rest of the Premier League to keep pace.
There were few if any positives to take from the game for Arsenal as they struggled to make an impression at Old Trafford.
For such a big game, the Gunners seemed to lack passion and again they lacked any penetration in the final third as they struggled to create chances.
The scoreline in the end flattered Arsenal as United should have won more convincingly.
Arsenal's defence also looked shaky with Kieran Gibbs sorely missed at left-back with Andre Santos again struggling to fill the void, while the normally reliable Thomas Vermaelen was well below-par.
The Gunners have now lost to title rivals Chelsea and United this season and it looks like the best they can hope for is a top four finish.